104With regard to the argument put forward by the Kingdom of Spain that the Commission is not entitled to find such an irregularity until case‑law clarified the point of law mentioned in paragraph 102 above, it must be borne in mind that the interpretation which the Court of Justice gives of a provision of EU law is limited to clarifying and defining the meaning and scope of that provision as it ought to have been understood and applied from the time of its entry into force. It follows that the provision as thus interpreted may, and must, be applied even to legal relationships which arose and were established before the judgment in question and it is only exceptionally that, in application of a general principle of legal certainty which is inherent in the Union legal order, the Court may decide to restrict the right to rely upon a provision, which it has interpreted, with a view to calling in question legal relationships established in good faith. Those considerations apply to the EU institutions when they, in turn, are required to implement the provisions of EU law which are subsequently interpreted by the Court of Justice (Case T-289/03BUPA and Others v Commission [2008] ECR II-81, paragraph 159).