We reproduce points 68 to 76 of the Opinion of Advocate General Wathelet on case C-362/12, Test Claimants in the FII Group Litigation
68. With effect at the latest from18 July 2003, the date on which the judgment in DMG was delivered, English law recognised the Kleinwort Benson cause of action as being available for the purposes of recovering taxes paid but not due, subject to the time limits laid down in section 32(1)(c) of the Limitation Act 1980.
69. At the hearing, the United Kingdom Government stressed the fact that, at the time when the judgment in DMG was delivered, it was not certain that that judgment would be confirmed on appeal, and that, accordingly, the companies belonging to the Aegis group could not at that time legitimately count on the ultimate success of their Kleinwort Benson claim.
70. That was not the issue for the companies belonging to the Aegis group. Rather, they submit that, when they lodged their claim on 8 September 2003, they could legitimately expect that their claim would be ruled upon by the English courts on the basis of the law in force on the date on which that claim was lodged.
71. On that point, I agree with Lord Hope and Lord Reed that the companies belonging to the Aegis group were entitled to expect, in accordance with the principles of legal certainty and the protection of legitimate expectations, that they would not be deprived of that right by a statute which, a few months after their claim was lodged, amended the related time limits without notice and with retroactive effect. (35)
72. In its application for a hearing, the United Kingdom Government refers to the amounts at stake in the present case. It submits that the reimbursement sought by the companies belonging to the Aegis group amounts to at least 2 billion pounds sterling and that the financial consequences for the tax authorities with regard to other claimants will amount to several billion pounds sterling. In its view, this raises a question of the protection of the public interest in preventing the disruption of public finances.
73. If the reimbursement of tax paid but not due is not to be treated differently depending on whether significant amounts are involved, that argument cannot be taken into consideration, since the Court has not, in declaring the taxes at issue here incompatible with EU law, restricted the temporal effects of its judgments.
74. It is settled case-law that the right to a refund of taxes levied in a Member State in breach of EU law is the consequence and complement of the rights conferred on individuals by provisions of EU law prohibiting such taxes. (36) There is only one exception to that obligation: where charges to tax have been passed on in their entirety to a third party and their reimbursement would bring about the unjust enrichment of the taxable person. (37) That is not the position here.
75. Furthermore, in its recent judgments in Irimie and Littlewoods Retail and Others, the Court held – on the basis of the case-law in Metallgesellschaft and Others and Test Claimants in the FII Group Litigation – that the Member States were under an obligation to repay with interest tax levied in breach of EU law. (38)
76. Consequently, the answer to Question 1 is that, where, under the law of a Member State, a taxpayer can choose between two causes of action in order to claim restitution of taxes levied contrary to Articles 49 TFEU and 63 TFEU and one of those causes of action benefits from a longer limitation period, the principles of effectiveness, legal certainty and the protection of legitimate expectations preclude legislation of that Member State, adopted after the claim has been brought, under which that longer limitation period is curtailed without notice and retrospectively.
Many thanks to Antonio Puentes for the tip.