38The Court of Justice has held that it must be accepted that the particularly sensitive and essential nature of the interests protected by Article 4(1)(a) of Regulation No 1049/2001, combined with the fact that access must be refused by the institution, under that provision, if disclosure of a document to the public would undermine those interests, confers on the decision which must thus be adopted by the institution a complex and delicate nature which calls for the exercise of particular care and that such a decision requires, therefore, a margin of appreciation (judgment of 1 February 2007, Sison v Council, C‑266/05 P, EU:C:2007:75, paragraph 35). This is corroborated by the fact that the exceptions set out in Article 4(1) of Regulation No 1049/2001 are framed in mandatory terms and it follows that the institutions are obliged to refuse access to documents falling under any one of those exceptions once the relevant circumstances are shown to exist and that there is no need to balance the protection of the public interest against an overriding general interest (see, to that effect, judgments of 25 April 2007, WWF European Policy Programme v Council, T‑264/04, EU:T:2007:114, paragraphs 44 and 45, and of 12 September 2013, Besselink v Council, T‑331/11, not published, EU:T:2013:419, paragraph 44).