Contents
Judgment of the Court (Grand Chamber)19 May 2026note[Text rectified by order of 8 July 2026](Reference for a preliminary ruling — Article 50 TEU — Article 288 TFEU — Agreement on the withdrawal of the United Kingdom of Great Britain and Northern Ireland from the European Union and the European Atomic Energy Community — Court of a Member State seised before the end of the transition period provided for in that agreement — Application by the courts of the forum of the law of another State — United Kingdom legislation transposing a directive — Directive 2006/54/EC — Applicability of EU law — Principle of mutual trust — Principle that national law must be interpreted in conformity with EU law)In Case C‑350/24,REQUEST for a preliminary ruling under Article 267 TFEU from the Cour de cassation (Court of Cassation, France), made by decision of 3 May 2024, received at the Court on 14 May 2024, in the proceedingsHJvCrédit agricole Corporate & Investment Bank SA,THE COURT (Grand Chamber),composed of K. Lenaerts, President, T. von Danwitz, Vice-President, F. Biltgen (Rapporteur), C. Lycourgos, I. Jarukaitis, I. Ziemele, J. Passer and O. Spineanu‑Matei, Presidents of Chambers, N. Piçarra, A. Kumin, N. Jääskinen, D. Gratsias, B. Smulders, S. Gervasoni and N. Fenger, Judges,Advocate General: J. Kokott,Registrar: C. Di Bella, Administrator,having regard to the written procedure and further to the hearing on 24 June 2025,after considering the observations submitted on behalf of:– HJ, by A. Lyon-Caen, avocat,– Crédit agricole Corporate & Investment Bank SA, by D. Célice, avocat,– the French Government, by F. du Couëdic, O. Duprat-Mazaré, B. Fodda, T. Lechevallier, H. Nunes da Silva and B. Travard, acting as Agents,– the Polish Government, by B. Majczyna and D. Lutostańska, acting as Agents,– the United Kingdom Government, by S. Fuller, acting as Agent, and by A. Mayer and J. Pobjoy, Barristers-at-Law,– the European Commission, by S. Delaude, H. Krämer and E.E. Schmidt, acting as Agents,after hearing the Opinion of the Advocate General at the sitting on 25 September 2025,gives the following
Judgment
1This request for a preliminary ruling concerns the interpretation of the Agreement on the withdrawal of the United Kingdom of Great Britain and Northern Ireland from the European Union and the European Atomic Energy Community (OJ 2020 L 29, p. 7), approved by Council Decision (EU) 2020/135 of 30 January 2020 (OJ 2020 L 29, p. 1) (‘the Withdrawal Agreement’), and of Article 288 TFEU.
2The request has been made in proceedings between HJ and her employer, Crédit agricole Corporate & Investment Bank SA (‘CACIB’), concerning discrimination on grounds of her sex and psychological harassment which she allegedly suffered.
Legal context
International law
3Article 70 of the Vienna Convention on the Law of Treaties of 23 May 1969 (United Nations Treaty Series, Vol. 1155, p. 331; ‘the Vienna Convention’), which is entitled ‘Consequences of the termination of a treaty’, provides, in paragraph 1 thereof:‘Unless the treaty otherwise provides or the parties otherwise agree, the termination of a treaty under its provisions or in accordance with the present Convention:(a) releases the parties from any obligation further to perform the treaty;(b) does not affect any right, obligation or legal situation of the parties created through the execution of the treaty prior to its termination.’
European Union law
The EU and FEU Treaties
4Article 50(2) and (3) TEU states:2. A Member State which decides to withdraw shall notify the European Council of its intention. In the light of the guidelines provided by the European Council, the [European] Union shall negotiate and conclude an agreement with that State, setting out the arrangements for its withdrawal, taking account of the framework for its future relationship with the Union. …3. The Treaties shall cease to apply to the State [which withdraws from the European Union] from the date of entry into force of the withdrawal agreement or, failing that, two years after the notification referred to in paragraph 2, unless the European Council, in agreement with the Member State concerned, unanimously decides to extend this period.’
5Article 288 TFEU provides:‘To exercise the Union’s competences, the institutions shall adopt regulations, directives, decisions, recommendations and opinions.A regulation shall have general application. It shall be binding in its entirety and directly applicable in all Member States.A directive shall be binding, as to the result to be achieved, upon each Member State to which it is addressed, but shall leave to the national authorities the choice of form and methods.A decision shall be binding in its entirety. A decision which specifies those to whom it is addressed shall be binding only on them.Recommendations and opinions shall have no binding force.’
The Withdrawal Agreement
6The second, seventh, eighth and eleventh paragraphs of the preamble to the Withdrawal Agreement state:‘WISHING to set out the arrangements for the withdrawal of the United Kingdom from the Union and Euratom, taking account of the framework for their future relationship,…RESOLVED to ensure an orderly withdrawal through various separation provisions aiming to prevent disruption and to provide legal certainty to citizens and economic operators as well as to judicial and administrative authorities in the Union and in the United Kingdom, while not excluding the possibility of relevant separation provisions being superseded by the agreement(s) on the future relationship,CONSIDERING that it is in the interest of both the Union and the United Kingdom to determine a transition or implementation period during which – notwithstanding all consequences of the United Kingdom’s withdrawal from the Union as regards the United Kingdom’s participation in the institutions, bodies, offices and agencies of the Union, in particular the end, on the date of entry into force of this Agreement, of the mandates of all members of institutions, bodies and agencies of the Union nominated, appointed or elected in relation to the United Kingdom’s membership of the Union – Union law, including international agreements, should be applicable to and in the United Kingdom, and, as a general rule, with the same effect as regards the Member States, in order to avoid disruption in the period during which the agreement(s) on the future relationship will be negotiated,…CONSIDERING that in order to guarantee the correct interpretation and application of this Agreement and compliance with the obligations under this Agreement, it is essential to establish provisions ensuring overall governance, in particular binding dispute-settlement and enforcement rules that fully respect the autonomy of the respective legal orders of the Union and of the United Kingdom as well as the United Kingdom’s status as a third country’.
7As set out in Article 1 of that agreement, headed ‘Objective’:‘This Agreement sets out the arrangements for the withdrawal of the United Kingdom … from the European Union … and from the European Atomic Energy Community …’
8Article 4 of that agreement, entitled ‘Methods and principles relating to the effect, the implementation and the application of this Agreement’, provides, in paragraphs 4 and 5:4. The provisions of this Agreement referring to Union law or to concepts or provisions thereof shall in their implementation and application be interpreted in conformity with the relevant case-law of the Court of Justice of the European Union handed down before the end of the transition period [referred to in Article 126 hereof (“the transition period”)].5. In the interpretation and application of this Agreement, the United Kingdom’s judicial and administrative authorities shall have due regard to relevant case-law of the Court of Justice of the European Union handed down after the end of the transition period.’
9Article 66 of that agreement, entitled ‘Applicable law in contractual and non-contractual matters’, which appears in Title VI of Part Three thereof, entitled ‘Ongoing judicial cooperation in civil and commercial matters’, is worded as follows:‘In the United Kingdom, the following acts shall apply as follows:(a) Regulation (EC) No 593/2008 of the European Parliament and of the Council [of 17 June 2008 on the law applicable to contractual obligations (Rome I) (OJ 2008 L 177, p. 6; ‘the Rome I Regulation’)] shall apply in respect of contracts concluded before the end of the transition period;(b) Regulation (EC) No 864/2007 of the European Parliament and of the Council [of 11 July 2007 on the law applicable to non-contractual obligations (Rome II) (OJ 2007 L 199, p. 40)] shall apply in respect of events giving rise to damage, where such events occurred before the end of the transition period.’
10Article 67 of the Withdrawal Agreement, headed ‘Jurisdiction, recognition and enforcement of judicial decisions, and related cooperation between central authorities’, provides:1.In the United Kingdom, as well as in the Member States in situations involving the United Kingdom, in respect of legal proceedings instituted before the end of the transition period and in respect of proceedings or actions that are related to such legal proceedings … the following acts or provisions shall apply:(a) the provisions regarding jurisdiction of Regulation (EU) No 1215/2012 [of the European Parliament and of the Council of 12 December 2012 on jurisdiction and the recognition and enforcement of judgments in civil and commercial matters (OJ 2012 L 351, p. 1)];(b) the provisions regarding jurisdiction of Regulation (EU) 2017/1001 [of the European Parliament and of the Council of 14 June 2017 on the European Union trade mark (OJ 2017 L 154, p. 1)], of [Council] Regulation (EC) No 6/2002 [of 12 December 2001 on Community designs (OJ 2002 L 3, p. 1)], of [Council] Regulation (EC) No 2100/94 [of 27 July 1994 on Community plant variety rights (OJ 1994 L 227, p. 1)], of Regulation (EU) 2016/679 of the European Parliament and of the Council of 27 April 2016 on the protection of natural persons with regard to the processing of personal data and on the free movement of such data, and repealing Directive 95/46/EC (General Data Protection Regulation) (OJ 2016 L 119, p. 1)], and of Directive 96/71/EC of the European Parliament and of the Council [of 16 December 1996 concerning the posting of workers in the framework of the provision of services (OJ 1997 L 18, p. 1)];(c) the provisions [regarding jurisdiction] of [Council] Regulation (EC) No 2201/2003 [of 27 November 2003 concerning jurisdiction and the recognition and enforcement of judgments in matrimonial matters and the matters of parental responsibility, repealing Regulation (EC) No 1347/2000 (OJ 2003 L 338, p. 1)];(d) the provisions [regarding jurisdiction] of [Council] Regulation (EC) No 4/2009 [of 18 December 2008 on jurisdiction, applicable law, recognition and enforcement of decisions and cooperation in matters relating to maintenance obligations (OJ 2009 L 7, p. 1)].…’
11Article 86 of the Withdrawal Agreement, headed ‘Pending cases before the Court of Justice of the European Union’, provides:1. The Court of Justice of the European Union shall continue to have jurisdiction in any proceedings brought by or against the United Kingdom before the end of the transition period. Such jurisdiction shall apply to all stages of proceedings, including appeal proceedings before the Court of Justice and proceedings before the General Court where the case is referred back to the General Court.2. The Court of Justice of the European Union shall continue to have jurisdiction to give preliminary rulings on requests from courts and tribunals of the United Kingdom made before the end of the transition period.3. For the purposes of this Chapter, proceedings shall be considered as having been brought before the Court of Justice of the European Union, and requests for preliminary rulings shall be considered as having been made, at the moment at which the document initiating the proceedings has been registered by the registry of the Court of Justice or the General Court, as the case may be.’
12Article 87 of that agreement, entitled ‘New cases before the Court of Justice’, is worded as follows:1. If the European Commission considers that the United Kingdom has failed to fulfil an obligation under the Treaties or under Part Four of this Agreement before the end of the transition period, the European Commission may, within 4 years after the end of the transition period, bring the matter before the Court of Justice of the European Union in accordance with the requirements laid down in Article 258 TFEU or the second subparagraph of Article 108(2) TFEU, as the case may be. The Court of Justice of the European Union shall have jurisdiction over such cases.2. If the United Kingdom does not comply with a decision referred to in Article 95(1) of this Agreement, or fails to give legal effect in the United Kingdom’s legal order to a decision, as referred to in that provision, that was addressed to a natural or legal person residing or established in the United Kingdom, the European Commission may, within 4 years from the date of the decision concerned, bring the matter to the Court of Justice of the European Union in accordance with the requirements laid down in Article 258 TFEU or the second subparagraph of Article 108(2) TFEU, as the case may be. The Court of Justice of the European Union shall have jurisdiction over such cases.3. In deciding to bring matters under this Article, the European Commission shall apply the same principles in respect of the United Kingdom as in respect of any Member State.’
13Under Article 126 of that agreement, entitled ‘Transition Period’, the transition period was to start on the date of entry into force of the Withdrawal Agreement and end on 31 December 2020.
14Article 127 of that agreement, headed ‘Scope of the transition’, is worded as follows:1. Unless otherwise provided in this Agreement, Union law shall be applicable to and in the United Kingdom during the transition period.…3. During the transition period, the Union law applicable pursuant to paragraph 1 shall produce in respect of and in the United Kingdom the same legal effects as those which it produces within the Union and its Member States, and shall be interpreted and applied in accordance with the same methods and general principles as those applicable within the Union.…6. Unless otherwise provided in this Agreement, during the transition period, any reference to Member States in the Union law applicable pursuant to paragraph 1, including as implemented and applied by Member States, shall be understood as including the United Kingdom.…’
15The fourth paragraph of Article 185 of the Withdrawal Agreement reads as follows:‘Parts Two and Three, with the exception of Article 19, Article 34(1), Article 44, and Article 96(1), as well as Title I of Part Six and Articles 169 to 181, shall apply as from the end of the transition period.’
The Rome Convention
16Article 3(1) of the Convention on the law applicable to contractual obligations opened for signature in Rome on 19 June 1980 (OJ 1980 L 266, p. 1) (‘the Rome Convention’) provides as follows:‘A contract shall be governed by the law chosen by the parties. The choice must be expressed or demonstrated with reasonable certainty by the terms of the contract or the circumstances of the case. By their choice the parties can select the law applicable to the whole or a part only of the contract.’
17Article 14(1) of the Rome Convention provides:‘The law governing the contract under this Convention applies to the extent that it contains, in the law of contract, rules which raise presumptions of law or determine the burden of proof.’
The Rome I Regulation
18Article 24 of the Rome I Regulation, entitled ‘Relationship with the Rome Convention’, provides:1. This Regulation shall replace the Rome Convention in the Member States, except as regards the territories of the Member States which fall within the territorial scope of that Convention and to which this Regulation does not apply pursuant to Article 299 [EC].2. In so far as this Regulation replaces the provisions of the Rome Convention, any reference to that Convention shall be understood as a reference to this Regulation.’
19In accordance with the second paragraph of Article 29 thereof, the Rome I Regulation is to apply from 17 December 2009 except for Article 26 thereof which is to apply from 17 June 2009.
Directive 2006/54/EC
20Recital 30 of Directive 2006/54/EC of the European Parliament and of the Council of 5 July 2006 on the implementation of the principle of equal opportunities and equal treatment of men and women in matters of employment and occupation (OJ 2006 L 204, p. 23) states:‘The adoption of rules on the burden of proof plays a significant role in ensuring that the principle of equal treatment can be effectively enforced. As the Court of Justice has held, provision should therefore be made to ensure that the burden of proof shifts to the respondent when there is a prima facie case of discrimination, except in relation to proceedings in which it is for the court or other competent national body to investigate the facts. It is however necessary to clarify that the appreciation of the facts from which it may be presumed that there has been direct or indirect discrimination remains a matter for the relevant national body in accordance with national law or practice. Further, it is for the Member States to introduce, at any appropriate stage of the proceedings, rules of evidence which are more favourable to plaintiffs.’
21Article 17 of that directive, entitled ‘Defence of rights’, provides, in paragraph 1:‘Member States shall ensure that, after possible recourse to other competent authorities including where they deem it appropriate conciliation procedures, judicial procedures for the enforcement of obligations under this Directive are available to all persons who consider themselves wronged by failure to apply the principle of equal treatment to them, even after the relationship in which the discrimination is alleged to have occurred has ended.’
22Article 19 of that directive, entitled ‘Burden of proof’, provides, in paragraphs 1 and 2:1. Member States shall take such measures as are necessary, in accordance with their national judicial systems, to ensure that, when persons who consider themselves wronged because the principle of equal treatment has not been applied to them establish, before a court or other competent authority, facts from which it may be presumed that there has been direct or indirect discrimination, it shall be for the respondent to prove that there has been no breach of the principle of equal treatment.2. Paragraph 1 shall not prevent Member States from introducing rules of evidence which are more favourable to plaintiffs.’
United Kingdom law
23Section 136 of the Equality Act 2010, entitled ‘Burden of proof’, provides:(1) This section applies to any proceedings relating to a contravention of this Act.(2) If there are facts from which the court could decide, in the absence of any other explanation, that a person (A) contravened the provision concerned, the court must hold that the contravention occurred.(3) But subsection (2) does not apply if A shows that A did not contravene the provision.’
The dispute in the main proceedings and the questions referred for a preliminary ruling
24The appellant in the main proceedings was employed by CACIB under a contract of employment concluded on 17 January 2007 and governed by United Kingdom law, under which she was most recently employed as a ‘customer information system officer in the United Kingdom’. From 28 August 2013, she was placed on sick leave.
25On 23 September 2013, taking the view that she had suffered discrimination on grounds of her sex and psychological harassment, the appellant in the main proceedings brought an action before a conseil de prud’hommes (Labour Tribunal, France) seeking payment of various sums in respect of performance of that employment contract and by way of compensation.
26By judgment of 26 June 2019, the conseil de prud’hommes (Labour Tribunal) dismissed the claims of the appellant in the main proceedings. She appealed against that judgment before the cour d’appel de Versailles (Court of Appeal, Versailles, France).
27By judgment of 27 May 2021, the cour d’appel de Versailles (Court of Appeal, Versailles) held that the appellant in the main proceedings had not demonstrated the existence of discrimination or discriminatory harassment and retaliation, within the meaning of the Equality Act 2010, which transposes Directive 2006/54 into United Kingdom law.
28The appellant in the main proceedings brought an appeal against that judgment before the Cour de cassation (Court of Cassation, France), which is the referring court. She submits, in particular, that, by holding, after examining each of the discriminatory situations relied on in turn, that she had failed to present primary facts capable of demonstrating discrimination, within the meaning of the Equality Act 2010, the cour d’appel de Versailles (Court of Appeal, Versailles) ruled on the basis of an interpretation of that legislation that was not in conformity with Article 19 of Directive 2006/54, which requires the court to carry out an overall appraisal of the facts in order to determine whether it may be presumed that there has been discrimination. Furthermore, in holding that the fact, relied on by the appellant in the main proceedings, that it was apparent from the documents submitted by her that the expatriate employees within CACIB were mainly men, provided insufficient grounds for presuming that there was discrimination against women in the absence of information on applications for such expatriation by women, that court of appeal also relied on an interpretation of the Equality Act 2010 which was not in conformity with Article 19 of Directive 2006/54, by placing on the appellant in the main proceedings the burden of proving the alleged discrimination.
29In the first place, the referring court notes that the dispute in the main proceedings raises the question of the impact of the withdrawal of the United Kingdom from the European Union on the powers and obligations of the court of a Member State that is required to apply United Kingdom law transposing a directive in the course of judicial proceedings brought before the end of the transition period, where the court hearing the case is called on to give its ruling after the end of that period. Although, on the date of the facts in the main proceedings or on the date on which the legal action concerned was brought by the appellant in the main proceedings and the date on which the conseil des prud’hommes (Labour Tribunal) ruled, the United Kingdom was still a member of the European Union, that was no longer the case on the date on which the Cour d’appel de Versailles (Court of Appeal, Versailles) ruled.
30In those circumstances, the referring court is uncertain whether EU law was applicable on the date on which the cour d’appel de Versailles (Court of Appeal, Versailles) ruled, since, on that date, subsequent to the date of the withdrawal of the United Kingdom from the European Union, EU law had ceased to have effect in the United Kingdom’s legal order. It also raises the question whether the Withdrawal Agreement retroactively called into question the application of EU law to disputes which arose before the end of the transition period and therefore the obligation for the court of a Member State to interpret the United Kingdom law applicable to those disputes in conformity with EU law. In that regard, the referring court puts forward two hypotheses: either the view could be taken that, after the end of the transition period, a certain body of EU law was maintained in United Kingdom law, but that there is no longer any obligation to interpret that law in conformity with EU law; or it could be considered that, since the facts in the main proceedings were prior to the end of the transition period and since the proceedings concerned had been brought before the end of that period, the United Kingdom legislation transposing Directive 2006/54, namely the Equality Act 2010, must be interpreted in conformity with EU law by the court of the forum even if it gives its ruling after the end of the transition period.
31In the second place, the referring court notes that the dispute in the main proceedings raises the question whether the principle that national law must be interpreted in conformity with EU law which is binding on the court of a Member State also applies where that court must apply the law of another Member State. It recalls that, according to the case-law of the Court, the principle of mutual trust requires each of the Member States, save in exceptional circumstances, to consider all the other Member States to be complying with EU law and particularly with the fundamental rights recognised by EU law (Opinion 2/13 (Accession of the European Union to the ECHR) of 18 December 2014, EU:C:2014:2454, paragraph 191). However, it is also apparent from that case-law that, in applying national law, whether the provisions in question were adopted before or after the directive concerned, the national court called upon to interpret it is required to do so, as far as possible, in the light of the wording and the purpose of the directive in order to achieve the result pursued by the latter and thereby comply with the third paragraph of Article 288 TFEU (judgment of 13 November 1990, Marleasing, C‑106/89, EU:C:1990:395, paragraph 8).
32The referring court takes the view that it cannot be ruled out that the same holds where that court is required to apply the law of another Member State. The Court’s case-law according to which it is for the court seised of a dispute to apply the legislation of the Member State whose courts are designated in a jurisdiction clause, interpreting that legislation in accordance with EU law, in particular a directive, supports such an approach (judgments of 18 November 2020, DelayFix, C‑519/19, EU:C:2020:933, paragraph 51, and of 8 December 2022, Luxury Trust Automobil, C‑247/21, EU:C:2022:966, paragraph 67). However, the Court has not yet ruled explicitly on such a question.
33In the third place, the referring court seeks to ascertain whether the powers and obligations of the court of a Member State applying the law of another Member State which finds it impossible to give an interpretation in conformity with EU law are the same as the powers and obligations which it exercises when it applies its own domestic law, and whether, as the case may be, the principle of non-discrimination enshrined in Article 21 of the Charter of Fundamental Rights of the European Union, as given concrete expression in Directive 2006/54, may, even in a dispute between individuals, lead it to disapply that law.
34In those circumstances, the Cour de cassation (Court of Cassation) decided to stay the proceedings and to refer the following questions to the Court of Justice for a preliminary ruling:(1) Must the [Withdrawal Agreement] be interpreted as meaning that United Kingdom legislation transposing Article 19 of [Directive 2006/54] must be regarded as legislation of a Member State transposing a directive, by a court giving its ruling after the end of the transition period, where the facts are prior to that date and/or the proceedings were brought before that date?(2) Must Article 288 TFEU be interpreted as meaning that a [court of a Member State,] hearing a dispute between individuals, which is obliged to apply the law of another Member State, must interpret the provisions of that law in conformity with a directive, without this being precluded by the principle of mutual trust?(3) If the [court of a Member State] considers that it is impossible to interpret those provisions in conformity with the directive, must it disapply [the law of that other Member State], as it would do with its own national law, where a general principle of EU law or a provision of primary law, as given concrete expression in a directive, is at issue?’
Consideration of the questions referred
Admissibility
35CACIB and the Commission contend that the questions referred by the referring court are inadmissible.
36They submit that it is apparent from the wording of section 136 of the Equality Act 2010 that that section contains a rule adjusting the burden of proof which is identical to that laid down in Article 19 of Directive 2006/54. Thus, section 136 is in conformity with EU law. They also consider that the question to be resolved by the referring court does not concern the interpretation of section 136 in the light of EU law, but only the manner in which the court adjudicating on the substance assessed the facts relied on by the appellant in the main proceedings in order to presume the existence of discrimination.
37CACIB submits that, in any event, first, the referring court does not provide the factual information accepted or rejected by the cour d’appel de Versailles (Court of Appeal, Versailles), or any information relating to the reasoning or analysis of that court and does not sufficiently explain the usefulness of the questions referred for the resolution of the dispute in the main proceedings. Therefore, those questions should be rejected as inadmissible, on the ground that they are general and hypothetical. Second, in accordance with the case-law of the referring court, that court does not have jurisdiction to review compliance, by appellate courts, with the interpretation and application of foreign law, since such a question constitutes a question of fact which is not subject to review by the referring court sitting as an appellate court. Third, the referring court does not have jurisdiction to make a reference to the Court of Justice for a preliminary ruling after the transition period.
38According to settled case-law, in proceedings under Article 267 TFEU, it is solely for the national court before which a dispute has been brought, and which must assume responsibility for the subsequent judicial decision, to determine, in the light of the particular circumstances of the case, both the need for a preliminary ruling in order to enable it to deliver judgment and the relevance of the questions which it submits to the Court of Justice. Consequently, where the questions submitted concern the interpretation of EU law, the Court of Justice is, in principle, required to give a ruling (judgments of 21 April 1988, Pardini, 338/85, EU:C:1988:194, paragraph 8, and of 24 July 2023, Lin, C‑107/23 PPU, EU:C:2023:606, paragraph 61 and the case-law cited).
39However, it is apparent from the actual wording of Article 267 TFEU that the question referred for a preliminary ruling must be necessary to enable the referring court to give judgment in the case before it. Thus, where it is quite obvious that the interpretation of EU law that is sought bears no relation to the actual facts of the main action or its purpose, where the problem is hypothetical, or where the Court does not have before it the factual or legal material necessary to give a useful answer to the questions submitted to it, the Court may refuse to rule on a question referred for a preliminary ruling by a national court (judgment of 16 May 2024, INSS (Leave for a mother in a single-parent family), C‑673/22, EU:C:2024:407, paragraphs 22, 23 and 25 and the case-law cited).
40Furthermore, according to settled case-law, in the context of the cooperation between the Court of Justice and the national courts, the need to provide an interpretation of EU law which will be of use to the national court means that the national court is bound to observe scrupulously the requirements concerning the content of a request for a preliminary ruling, expressly set out in Article 94 of the Rules of Procedure of the Court of Justice. In particular, it is essential that, as is stated in Article 94(c) of the Rules of Procedure, the order for reference contain a statement of the reasons which prompted the national court to inquire about the interpretation of certain provisions of EU law, and the relationship between those provisions and the national legislation applicable to the main proceedings (see, to that effect, judgment of 28 November 2023, Commune d’Ans, C‑148/22, EU:C:2023:924, paragraphs 44 and 46 and the case-law cited).
41In the present case, it is apparent from the request for a preliminary ruling that the referring court is uncertain, in the context of a dispute before it, of the impact of the withdrawal of the United Kingdom from the European Union on the powers and obligations of the court of a Member State that is required to apply United Kingdom law transposing a directive in the course of judicial proceedings brought before the end of the transition period, where the court hearing the case is called on to give its ruling after the end of that period. The referring court notes, moreover, that the dispute in the main proceedings raises the question whether the principle that national law must be interpreted in conformity with EU law which is binding on the court of a Member State applies where that court must apply the law of another Member State.
42As regards, in the first place, CACIB’s argument that the referring court does not have jurisdiction to refer to the Court, after the end of the transition period, a reference for a preliminary ruling concerning whether the interpretation of United Kingdom law which transposes a directive into its domestic legal order is in conformity, it is sufficient to note that the questions submitted by the referring court concern the interpretation of EU law, including the Withdrawal Agreement, which forms part of that law. Therefore, in accordance with Article 267 TFEU, the referring court, which is a court or tribunal of a Member State adjudicating at last instance, was entitled and, in principle, obliged to make a reference to the Court of Justice for a preliminary ruling. Article 86(2) of the Withdrawal Agreement confers on the Court the necessary jurisdiction to give preliminary rulings on requests made before the end of the transition period by the courts and tribunals of the United Kingdom, since, after the withdrawal of that State from the European Union, Article 267 TFEU is no longer applicable to its courts and tribunals. Article 86(2) cannot be interpreted in such a way as to preclude the possibility or, as the case may be, the obligation of the courts of the Member States to make a reference to the Court of Justice for a preliminary ruling for the purposes of interpreting EU law in cases connected with the United Kingdom.
43In the second place, it must be stated that the referring court has not set out, as required by Article 94(c) of the Rules of Procedure, the reasons why it considers that it is impossible to interpret the Equality Act 2010 in conformity with EU law and, therefore, why an answer to that question is necessary to enable it to give judgment in the case before it.
44In those circumstances, as regards the third question, which concerns that situation, the Court does not have the necessary material to provide a useful answer to the referring court. That question must therefore be declared inadmissible.
45In the third place, by its first and second questions, the referring court seeks, in essence, to determine whether the applicability of EU law to a dispute such as that in the main proceedings has been called into question by the Withdrawal Agreement and, if that is not the case, whether a court of a Member State must interpret the law of another Member State or of a State treated as such which is applicable to the dispute before it in conformity with EU law.
46An answer to the first question, concerning the applicability of EU law, appears necessary in order to enable the referring court to give judgment in the case before it. In those circumstances, the objection alleging that EU law is not applicable does not concern the admissibility of the request for a preliminary ruling but concerns the substance of the question referred.
47Moreover, CACIB’s argument that the referring court does not have jurisdiction, according to its own case-law, to review appellate courts’ compliance with the interpretation and application of foreign law cannot affect the admissibility of the second question in so far as that argument concerns the interpretation of national law, which falls within the exclusive jurisdiction of that court.
48The first and second questions are therefore admissible.
Substance
The first question
49By its first question, the referring court asks, in essence, whether Article 50(3) TEU, read in conjunction with Articles 126 and 127 of the Withdrawal Agreement, must be interpreted as meaning that that agreement has called into question the applicability of Article 19 of Directive 2006/54 to a dispute which was pending on the date of the end of the transition period and relates to alleged acts of discrimination which occurred before that date in the context of the performance of an employment contract governed by United Kingdom law.
50It should be recalled that, in accordance with Article 50(3) TEU, the Treaties are to cease to apply to the State which withdraws from the European Union from the date of entry into force of the withdrawal agreement or, failing that, two years after the notification of withdrawal, unless the European Council, in agreement with the Member State concerned, unanimously decides to extend this period.
51Thus, under Article 50(3) TEU, the Treaties ceased to apply to the United Kingdom on the date on which the Withdrawal Agreement entered into force, on 1 February 2020, so that that State is no longer, as from that date, a Member State (judgment of 9 June 2022, Préfet du Gers and Institut national de la statistique et des études économiques, C‑673/20, EU:C:2022:449, paragraph 55 and the case-law cited).
52However, in accordance with the seventh paragraph of its preamble, the objective of the Withdrawal Agreement is to ensure an orderly withdrawal through various separation provisions aiming to prevent disruption and to provide legal certainty to citizens and economic operators as well as to judicial and administrative authorities in the Union and in the United Kingdom.
53In that regard, the Withdrawal Agreement expressly provides for the extension of the application of EU law to the United Kingdom, with a few exceptions, until 31 December 2020, the date of the end of the transition period. The eighth paragraph of the preamble to the Withdrawal Agreement states that it is in the interest of both the Union and the United Kingdom to determine a transition period during which Union law, including international agreements, should be applicable to and in the United Kingdom, and, as a general rule, with the same effect as regards the Member States, in order to avoid disruption in the period during which the agreement(s) on the future relationship will be negotiated.
54Under Article 126 of the Withdrawal Agreement, the transition period, governed by Part Four of that agreement, ran from the date of entry into force of that agreement, namely 1 February 2020, until 31 December 2020. Article 127(1) of that agreement states that, unless otherwise provided, during that period, Union law is to be applicable to and in the United Kingdom. Article 127(3) of the Withdrawal Agreement further provides that, during that period, the Union law applicable pursuant to paragraph 1 is to produce in respect of and in the United Kingdom the same legal effects as those which it produces within the Union and its Member States, and is to be interpreted and applied in accordance with the same methods and general principles as those applicable within the Union. In addition, Article 127(6) of that agreement states that unless otherwise provided in the Agreement, during that period, any reference to Member States in the Union law applicable pursuant to paragraph 1, including as implemented and applied by Member States, is to be understood as including the United Kingdom.
55It should be noted, in the first place, that the Withdrawal Agreement does not contain any general provision governing the applicability of EU law to disputes pending at the end of the transition period which relate to contractual relationships which arose before that date.
56That said, the Withdrawal Agreement expressly recognises that EU law may apply even after the end of the transition period to certain contractual relationships and disputes. The fourth paragraph of Article 185 of the Withdrawal Agreement provides that, as from the end of the transition period, (i) Parts Two and Three thereof – which include Articles 9 to 125 of that agreement – are to apply, with the exception of Article 19, Article 34(1), Article 44 and Article 96(1) thereof, and (ii) Title I of Part Six of that agreement, which includes Articles 158 to 163 thereof, and Title III of Part Six of that agreement, which includes Articles 169 to 181 thereof, are to apply.
57Part Three of the Withdrawal Agreement, entitled ‘Separation provisions’, provides, inter alia, in Title VI thereof, entitled ‘Ongoing judicial cooperation in civil and commercial matters’, that, after the end of the transition period, certain rules of Union law continue to apply to disputes which arose before the end of that period and which are still pending after the end of that period.
58That is the case, in particular, as stated in Article 66 of the Withdrawal Agreement, with regard to the Rome I Regulation, which continues to apply in the United Kingdom in respect of contracts concluded before the end of the transition period, and with regard to Regulation No 864/2007 in respect of events giving rise to damage which occurred before that date.
59Similarly, Article 67 of the Withdrawal Agreement provides that certain rules of Union law on jurisdiction and the enforcement of judgments continue to apply to judicial proceedings which were instituted before the end of the transition period. Thus, the courts of the Member States may have to recognise the jurisdiction of the United Kingdom courts, and Member States must, in principle, enforce certain judgments of those courts.
60It follows, therefore, from the general scheme of the Withdrawal Agreement that the parties to that agreement wished to preserve the stability of legal situations existing before the end of the transition period in accordance with the principle of legal certainty.
61In that regard, it is true, as is apparent from the second and eleventh paragraphs of the preamble to the Withdrawal Agreement, that that agreement was concluded with a view to setting out the arrangements for the withdrawal of the United Kingdom, inter alia, from the European Union ‘taking account of the framework for their future relationship’, while ‘fully respect[ing] the autonomy of the respective legal orders of the Union and of the United Kingdom as well as the United Kingdom’s status as a third country’, EU law, including its general principles and inter alia the principle of legal certainty, no longer as a rule being applicable to that country after the transition period. That said, it must be borne in mind that the legal basis of that agreement is Article 50 TEU, paragraph 2 of which confers on the European Union competence to negotiate and conclude an agreement laying down the detailed rules for withdrawal which is intended to regulate, in all the areas covered by the Treaties, all questions relating to the separation between the European Union and the State withdrawing from it (see, to that effect, judgment of 16 November 2021, Governor of Cloverhill Prison and Others, C‑479/21 PPU, EU:C:2021:929, paragraphs 48 and 50). In those circumstances, it must be held that, by that agreement, those parties intended, for that purpose, to implement, inter alia, the principle of legal certainty as forming part of EU law.
62Thus, the Withdrawal Agreement must be interpreted in the light of the principle of legal certainty, compliance with which that agreement seeks to ensure.
63According to settled case-law, the principle of legal certainty, the corollary of which is the principle of the protection of legitimate expectations, requires that rules of law be clear and precise and that the application of those rules be predictable for individuals, especially where they may have negative consequences for individuals and undertakings (see, to that effect, judgments of 2 December 2009, Aventis Pasteur, C‑358/08, EU:C:2009:744, paragraph 47, and of 5 September 2024, Novo Banco and Others, C‑498/22 to C‑500/22, EU:C:2024:686, paragraph 95).
64The principle of legal certainty precludes a new substantive legal rule from applying retroactively, namely to a situation established prior to its entry into force, and requires that any factual situation should normally, in the absence of any express contrary provision, be examined in the light of the legal rules existing at the time when the situation obtained (see, to that effect, judgment of 29 July 2024, Twenty First Capital, C‑174/23, EU:C:2024:654, paragraph 59 and the case-law cited).
65It follows that, in accordance with the principle of legal certainty, compliance with which the Withdrawal Agreement seeks to ensure, that agreement cannot, in the absence of an express provision, be interpreted as meaning that the European Union and the United Kingdom have agreed to terminate retroactively the application of almost all EU law to legal relationships which arose from a contract governed by United Kingdom law concluded before the end of the transition period.
66It should also be noted that Article 50(3) TEU does not expressly state that EU law is no longer applicable to pre-existing situations in the State concerned after that State’s withdrawal from the European Union.
67Such an interpretation is supported by Article 70(1) of the Vienna Convention, which governs the termination of international treaties and which, as the Advocate General pointed out in point 58 of her Opinion, codifies customary international law.
68Even though the Vienna Convention does not bind either the European Union or all its Member States, certain provisions in that convention reflect the rules of customary international law that, as such, are binding upon the EU institutions and are part of the EU legal order (see, to that effect, judgments of 16 June 1998, Racke, C‑162/96, EU:C:1998:293, paragraphs 24, 45 and 46; of 25 February 2010, Brita, C‑386/08, EU:C:2010:91, paragraph 42; and of 27 February 2018, Western Sahara Campaign UK, C‑266/16, EU:C:2018:118, paragraph 58).
69Although, like Article 50(3) TEU, the Vienna Convention provides, in Article 70(1)(a) thereof, that the termination of an international treaty releases the parties from any obligation further to perform it, subparagraph (b) of that provision specifies that such termination does not affect the rights and obligations of the parties flowing, prior to the termination of that Treaty, from the execution of that treaty and the legal situation thus created. Article 70(1) of the Vienna Convention specifies, moreover, that those principles apply unless that Treaty otherwise provides or the parties otherwise agree.
70In those circumstances, in view of the fundamental importance of the principle of legal certainty, it cannot, in the absence of an express provision in the Treaties and in the Withdrawal Agreement, be considered that the European Union and the United Kingdom have agreed to terminate retroactively the application of EU law to a dispute which was pending on the date of the end of the transition period and relates to alleged acts of discrimination which occurred before that date in the context of the performance of an employment contract governed by United Kingdom law.
71In the second place, as regards, more specifically, the rule set out in Article 19 of Directive 2006/54, recital 30 of that directive states that the adoption of rules on the burden of proof plays a significant role in ensuring that the principle of equal treatment can be effectively enforced. As a result, Article 19(1) of that directive cannot be regarded as laying down a mere procedural rule which ceases to apply to the United Kingdom at the end of the transition period. Rather, the rule set out in Article 19(1) is a substantive legal rule governing the employment relationship created by a contract concluded before the end of the transition period, with the result that that rule continues to apply, even after the end of that period, to disputes concerning that relationship.
72Any interpretation to the contrary would result in a serious limitation of the scope of the principle of legal certainty and of the effective implementation of the principle of equal treatment, which is covered by Directive 2006/54. The extent of the protection conferred by that directive would then depend on the fortuitous circumstance whether or not the proceedings relating to the rights and obligations created by that directive were concluded before the end of the transition period. Thus, an individual who, like the appellant in the main proceedings, brought his or her action before the competent courts of a Member State before the end of the transition period, and therefore when there was no doubt that United Kingdom law had to be interpreted in accordance with EU law, could no longer, on the sole ground that the national court concerned gave its ruling after the end of the transition period, rely before that court on the rights conferred on him or her by EU law.
73In the light of all of the foregoing, the answer to the first question is that Article 50(3) TEU, read in conjunction with Articles 126 and 127 of the Withdrawal Agreement, must be interpreted as meaning that that agreement has not called into question the applicability of Article 19 of Directive 2006/54 to a dispute which was pending on the date of the end of the transition period and relates to alleged acts of discrimination which occurred before that date in the context of the performance of an employment contract governed by United Kingdom law.
The second question
74By its second question, the referring court asks, in essence, whether Article 288 TFEU must be interpreted as meaning that, where a court of a Member State interprets and applies the law of another Member State which implements a directive, it is required, as it is when interpreting and applying its own law, to observe the principle that national law must be interpreted in conformity with EU law.
–The obligation, on the part of the courts of a Member State, to observe the principle that national law must be interpreted in conformity with EU law when applying the law of another Member State
75It should be noted that EU law is characterised by the fact that it stems from an independent source of law, the Treaties, by its primacy over the laws of the Member States and by the direct effect of a whole series of provisions which are applicable to their nationals and to the Member States themselves. These essential characteristics of EU law have given rise to a structured network of principles, rules and mutually interdependent legal relations linking the European Union and its Member States, and its Member States with each other (judgments of 6 March 2018, Achmea, C‑284/16, EU:C:2018:158, paragraph 33, and of 24 June 2019, Popławski, C‑573/17, EU:C:2019:530, paragraph 52 and the case-law cited).
76The principle of the primacy of EU law establishes the pre-eminence of EU law over the law of the Member States. That principle therefore requires all bodies of those States to give full effect to the various EU provisions, and the law of those States may not undermine the effect accorded to those various provisions in the territory of those States (judgment of 24 June 2019, Popławski, C‑573/17, EU:C:2019:530, paragraphs 53 and 54 and the case-law cited).
77In order to ensure the effectiveness of all provisions of EU law, the primacy principle requires, inter alia, the courts of the Member States to interpret, to the greatest extent possible, their national law in conformity with EU law (judgment of 24 June 2019, Popławski, C‑573/17, EU:C:2019:530, paragraph 57).
78That principle of interpretation in conformity with EU law is inherent in the system of the Treaties, since it permits a court of a Member State, within the limits of its jurisdiction, to ensure the full effectiveness of EU law when it determines the dispute before it (judgment of 24 June 2019, Popławski, C‑573/17, EU:C:2019:530, paragraph 55 and the case-law cited).
79According to settled case-law, a directive cannot of itself impose obligations on an individual and cannot therefore be relied on as such against an individual (judgments of 5 October 2004, Pfeiffer and Others, C‑397/01 to C‑403/01, EU:C:2004:584, paragraph 108, and of 19 January 2010, Kücükdeveci, C‑555/07, EU:C:2010:21, paragraph 46). However, the Member States’ obligation arising from a directive to achieve the result envisaged by that directive and their duty to take all appropriate measures, whether general or particular, to ensure the fulfilment of that obligation are binding on all the authorities of the Member State, including, for matters within their jurisdiction, the courts (see, to that effect, judgments of 10 April 1984, von Colson and Kamann, 14/83, EU:C:1984:153, paragraph 26; of 5 October 2004, Pfeiffer and Others, C‑397/01 to C‑403/01, EU:C:2004:584, paragraph 110; and of 19 January 2010, Kücükdeveci, C‑555/07, EU:C:2010:21, paragraph 47).
80It follows that the courts of the Member States are bound, when they apply their domestic law, and in particular legislative provisions specifically adopted in order to implement the requirements of a directive, to interpret it, so far as possible, in the light of the wording and the purpose of that directive in order to achieve the result sought by the directive and consequently comply with the third paragraph of Article 288 TFEU (judgments of 5 October 2004, Pfeiffer and Others, C‑397/01 to C‑403/01, EU:C:2004:584, paragraph 113, and of 12 December 2024, Getin Holding and Others, C‑118/23, EU:C:2024:1013, paragraph 75).
81It is true that the Court has held that the principle of interpretation of national law in conformity with EU law has certain limits. Thus, the obligation on a national court to refer to the content of a directive when interpreting and applying the relevant rules of its domestic law is limited by general principles of law, particularly those of legal certainty and non-retroactivity, and that obligation cannot serve as the basis for an interpretation of the national law concerned contra legem (judgments of 4 July 2006, Adeneler and Others, C‑212/04, EU:C:2006:443, paragraph 110, and of 5 June 2025, Nuratau, C‑349/24, EU:C:2025:397, paragraph 45).
82Nevertheless, the principle that national law must be interpreted in conformity with EU law requires the courts of the Member States to do whatever lies within their jurisdiction, taking the whole body of their domestic law into consideration and applying the interpretative methods recognised by domestic law, with a view to ensuring that the directive in question is fully effective and achieving an outcome consistent with the objective pursued by it (judgments of 4 July 2006, Adeneler and Others, C‑212/04, EU:C:2006:443, paragraph 111, and of 5 June 2025, Nuratau, C‑349/24, EU:C:2025:397, paragraph 46 and the case-law cited).
83If such an interpretation is not possible, the courts of the Member States are required, for matters within their jurisdiction, to provide the legal protection which individuals derive from EU law and to ensure that EU law is fully effective, if necessary disapplying of their own motion any provision of national law which is contrary to a provision of EU law which has direct effect in the dispute before them (see, to that effect, judgments of 24 June 2019, Popławski, C‑573/17, EU:C:2019:530, paragraph 61, and of 12 December 2024, Getin Holding and Others, C‑118/23, EU:C:2024:1013, paragraph 76).
84Where a court of a Member State, hearing a dispute between individuals, is called upon to apply the legislation of another Member State implementing a directive, it is required, in compliance with the general principles of law, to interpret the provisions of that legislation in conformity with EU law.
85In that regard, the Court has already held that it is for the court of a Member State, seised of a dispute involving the validity of a jurisdiction clause, which must, in accordance with Article 25(1) of Regulation No 1215/2012, be assessed under the legislation of the Member State whose courts are designated in that clause, to apply that legislation by interpreting it in accordance with EU law (see, to that effect, judgment of 18 November 2020, DelayFix, C‑519/19, EU:C:2020:933, paragraph 51).
86In addition, the Court held that an Austrian court hearing a dispute concerning value added tax (VAT) is under an obligation to interpret the law applicable to that dispute, whether it be the law of the Member State of the intermediary acquiring the goods or that of the final customer, in accordance with EU law (see, to that effect, judgment of 8 December 2022, Luxury Trust Automobil, C‑247/21, EU:C:2022:966, paragraph 67).
87It follows that, in the context of a dispute such as that in the main proceedings, where, under the rules of the Rome Convention, which the Rome I Regulation replaced, the courts of a Member State seised of a dispute must apply the law of another Member State, they are required to observe, as regards the law of that other Member State, the principle that national law must be interpreted in conformity with EU law.
88It should be added that the application of the principle that national law must be interpreted in conformity with EU law, in so far as it seeks to ensure that decisions given by the authorities and courts of the Member States are consistent with EU law, contributes to observance of the principle of mutual trust between the Member States, the latter principle being, in EU law, of fundamental importance (Opinion 2/13 (Accession of the European Union to the ECHR) of 18 December 2014, EU:C:2014:2454, paragraph 191).
89That principle of mutual trust requires each of the Member States, save in exceptional circumstances, to consider all the other Member States to be complying with EU law (see, to that effect, judgment of 19 December 2024, Tudmur, C‑185/24 and C‑189/24, EU:C:2024:1036, paragraph 31 and the case-law cited). It follows that a court of a Member State which interprets a provision of the law of another Member State in conformity with EU law is merely doing what it is entitled to presume, in accordance with the principle of mutual trust, the courts of that other Member State would do if they were called upon to interpret that provision.
90Consequently, the principle of mutual trust imposes on the courts of the Member States a duty of trust as regards the correct application, in the other Member States, of EU law. In particular, where those courts apply the law of another Member State, in a dispute in civil and commercial matters, under the rules of the Rome Convention, which the Rome I Regulation replaced, they endeavour, in accordance with the principles applicable to the powers and obligations of the court of the forum, to investigate the content of the law of that other Member State and the interpretation given to it by the courts of that other Member State and must presume that that law and that interpretation are in conformity with EU law.
91[As rectified by order of 8 July 2026] Thus, if the courts of a Member State have serious doubts as to whether the legislation of another Member State is in conformity with a directive which it transposes, those courts must satisfy themselves as to the interpretation to be given to that legislation by using, where appropriate, the mechanisms for judicial cooperation, in particular the mechanisms for obtaining information on foreign law, such as the European Judicial Network in civil and commercial matters established by Council Decision 2001/470/EC of 28 May 2001 establishing a European Judicial Network in civil and commercial matters (OJ 2001 L 174, p. 25), or the European Convention on Information on Foreign Law of 7 June 1968 (United Nations Treaty Series, Vol. 720-II, No 10346, p. 147).
92If doubts remain, those courts also have the option, or even the obligation, depending on the circumstances, to request a preliminary ruling from the Court. Indeed, the Court has held that, where there are questions intended to enable a court of a Member State to determine whether provisions of another Member State are compatible with EU law, the Court may provide the criteria for the interpretation of EU law which will enable a court of a Member State to resolve the legal issue before it (see, to that effect, judgment of 23 November 1989, Eau de Cologne & Parfümerie-Fabrik 4711, C‑150/88, EU:C:1989:594, paragraph 12 and the case-law cited).
93It follows from those considerations that, in accordance with the principle of mutual trust, the review of whether the law of a Member State is in conformity with EU law rests primarily with the courts of that Member State and, in the alternative, with the courts of the other Member States which are, where appropriate, called upon to apply the national law concerned to a dispute before them.
94Where, under the rules of the Rome I Regulation or, as in the case in the main proceedings, those of the Rome Convention, a court of a Member State is called upon to apply the law of another Member State to a dispute before it, it must satisfy itself that EU law has been complied with and it is therefore required, like the court of that other Member State, to apply the national law concerned in conformity with EU law and, where appropriate, to disapply any provision of the national law concerned which it considers cannot be applied in conformity with EU law.
95The foregoing considerations also apply where, as in the dispute in the main proceedings, a court of a Member State is called upon to apply United Kingdom legislation implementing Article 19 of Directive 2006/54 to a dispute which was pending on the date of the end of the transition period referred to in Article 126 of the Withdrawal Agreement and relates to alleged acts of discrimination which occurred before that date in the context of the performance of an employment contract governed by United Kingdom law which was concluded before the end of the transition period referred to in Article 126 of the Withdrawal Agreement. As is apparent from the answer to the first question, Article 19 remains applicable to that dispute even after the end of that period.
–Review of compliance, by the courts of a Member State, with the principle that national law must be interpreted in conformity with EU law when applying the law of another Member State
96It follows from the order for reference and the written observations submitted to the Court that, in the appeal on a point of law which it brought before the referring court, the appellant in the main proceedings complains that the judgment of the cour d’appel de Versailles (Court of Appeal, Versailles) contains an interpretation of United Kingdom law applicable to the dispute in the main proceedings which is not in conformity with EU law, in particular Directive 2006/54.
97In accordance with the settled case-law of the referring court mentioned in the order for reference, ‘courts adjudicating on the substance have absolute discretion in applying and interpreting foreign law’. It is apparent, moreover, from the documents before the Court that the task of a court hearing an appeal on a point of law is limited to reviewing defects in the statement of reasons and distortion of foreign law, with the result that that task is limited to reviewing whether the courts adjudicating on the substance have investigated the content of that law, without being empowered to criticise errors in the interpretation or application of that law.
98At the hearing before the Court, the French Government stated that, although, according to the settled case-law of the referring court, that court classifies the law of another State as a ‘rule of law’, it treats that law as a factual matter, with the result that, when it is seised, in the context of an appeal on a point of law, of a dispute coming under that foreign law, its review of whether the courts adjudicating on the substance have applied that foreign law in conformity with EU law is limited.
99Consequently, it is apparent that, where the referring court is seised of a dispute between individuals coming under the law of another Member State or of a State treated as such, the possibility of reviewing, in the context of an appeal on a point of law, whether the courts adjudicating on the substance have applied that law in conformity with EU law is also limited.
100As is apparent from the foregoing considerations, Article 288 TFEU must be interpreted as meaning that, where a court of a Member State interprets and applies the law of another Member State which implements a directive, it is required, as it is when interpreting and applying its own law, to observe the principle that national law must be interpreted in conformity with EU law.
101Unless one were to disregard the obligation, arising from the third paragraph of Article 288 TFEU, that all the authorities of the Member States, including the courts and tribunals, are required to achieve the result prescribed by a directive, the review carried out by a court hearing an appeal on a point of law in response to a plea alleging that a lower court or tribunal has interpreted the law of another Member State in breach of a directive cannot be limited solely on the ground that, as a general rule, that court or tribunal treats foreign law as a factual matter. That review must relate to whether the lower court has complied with the obligation to interpret in conformity with the result prescribed by the directive, which, as is apparent from paragraphs 84 and 94 of the present judgment, exists irrespective of whether the law to be interpreted is that of the forum or of another Member State.
102In the light of all of the foregoing, the answer to the second question is that Article 288 TFEU must be interpreted as meaning that where a court of a Member State interprets and applies the law of another Member State which implements a directive, it is required, as it is when interpreting and applying its own law, to observe the principle that national law must be interpreted in conformity with EU law.
Costs
103Since these proceedings are, for the parties to the main proceedings, a step in the action pending before the referring court, the decision on costs is a matter for that court. Costs incurred in submitting observations to the Court, other than the costs of those parties, are not recoverable.
Operative part
On those grounds, the Court (Grand Chamber) hereby rules:
1.Article 50(3) TEU, read in conjunction with Articles 126 and 127 of the Agreement on the withdrawal of the United Kingdom of Great Britain and Northern Ireland from the European Union and the European Atomic Energy Community, approved by Council Decision (EU) 2020/135 of 30 January 2020,must be interpreted as meaning that that agreement has not called into question the applicability of Article 19 of Directive 2006/54/EC of the European Parliament and of the Council of 5 July 2006 on the implementation of the principle of equal opportunities and equal treatment of men and women in matters of employment and occupation to a dispute which was pending on the date of the end of the transition period referred to in Article 126 and relates to alleged acts of discrimination which occurred before that date in the context of the performance of an employment contract governed by United Kingdom law.
2.Article 288 TFEUmust be interpreted as meaning that where a court of a Member State interprets and applies the law of another Member State which implements a directive, it is required, as it is when interpreting and applying its own law, to observe the principle that national law must be interpreted in conformity with EU law.
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