As to the fourth question, in which the court making the reference inquiries whether Community law contains any rules which are relevant in the present case for the purpose of deciding the question of the repayment of taxes paid contrary to Article 95 and whether in this connexion it is of any relevance that a trader can establish that he has suffered damage, the following comments may be made:

both parties in the main action agree that a claim for repayment based on the fact that the national provisions are incompatible with Community law are, in principle, decided according to national rules. Danish legislation is special in this respect in that there is no express legal provision for the repayment of overpaid taxes. According to the consistent case-law of the Danish courts the criterion of unjust enrichment plays a decisive role in answering the question whether payments made in error or without good reason must be refunded. Apparently there can only be a claim for repayment if the enrichment has gone to the disadvantage of the party which has made the payment.

The plaintiff in the main action is of the opinion that the repayment of taxes paid but not owed is too obscurely drafted in Danish law. The legal uncertainty which this creates is, in particular, it claims, incompatible with the protection granted by Community law in this field to Danish members of the EEC. It must also be noted in this connexion that according to Danish law taxpayers cannot avoid the duty to pay taxes in the absence of a judgment from the courts. Moreover, it is extremely difficult to furnish evidence that damage has been suffered as a result of the difficult market conditions, which means that an application has small chances of success. However if Community law is to be effective it is necessary to grant the undertakings affected an unrestricted claim to repayment. The repayment should be made from the date on which Danish law came into conflict with Community law, that is to say, the date of the accession of Denmark to the European Economic Community. At the very least, the excess taxes should be refunded as from the date on which the complaint or application was lodged.

The first observation made by the Danish Government is that the fourth question has no relevance because the Danish system is compatible with Community law. In the alternative, it observes that even Community law contains no express rules governing the repayment of taxes wrongfully levied. It follows however from the case-law of the Court of Justice on the direct effect of Community law that in principle a claim to repayment of taxes paid contrary to Community law exists. In accordance with the principle of the duty of cooperation enunciated in Article 5 of the EEC Treaty, the task of affording the protection of the law falls to the domestic courts. Thus it is equally the task of those courts to decide, taking into account the limits prescribed by Community law, whether and to what extent a repayment is to be made. According to the established case-law of the Danish courts, which does not by any means lead to uncertainty in the law, repayment depends decisively on whether the taxpayer has suffered damage. However, the plaintiff in the main action has no claim to repayment of the tax paid since this prerequisite for a claim to repayment is not satisfied. The truth is that in the end the taxes have been passed on to the consumer, with the consequence that the plaintiff in the main action would be unjustly enriched by the repayment.

Together with the Danish Government, the Commission is also of the opinion that Community law requires repayment of taxes paid but not owed but that in the absence of provisions of Community law the extent of the protection by the law in that respect depends on domestic law, taking into account merely the limits which have been set by Community law.

The view thus put forward by the Danish Government and the Commission must, so much can already be said from the outset, be accepted for the following reasons :

As the Court of Justice has consistently held in decided cases, most recently in its judgment of 22 March 1977 in Case 74/76 (Iannelli & Volpi S.pA. v Firma Paolo Meroni [1977] ECR 557), Article 95 of the Treaty has direct effect and creates individual rights which the courts of the Member States must protect (see Case 57/65, Firma Alfons Lütticke GmbH v Hauptzollamt Saarlouis, judgment of 16 June 1966, [1966] ECR 205, and Case 45/75, REWE). The consequence of this direct effect is that from the moment of Denmark's accession, that is to say, from 1 January 1973, those subject to the law may rely before the national courts on the provision laid down in the first paragraph of Article 95, which in this connexion takes precedence over national rules to the contrary. If individuals rely upon this provision the levying of charges which are contrary to Article 95 must be declared inadmissible. If the charges contrary to the provision have already been paid, then, as I have already pointed out in my opinion in Case 77/76 (Firma Gebr. Cucchi v Avez S.p.A., judgment of 25 May 1977 [1977] ECR 987), from the point of view of Community law the direct effect of that provision involves in addition that they should be repaid. The duty to afford this legal protection, which springs for citizens from the direct effect of Community law, devolves, as the Court of Justice declared in Case 33/76 (REWE-Zentralfinanz eG and REWE-Zentral AG v Landwirtschaftskammer für das Saarland, judgment of 16 December 1976 [1976] ECR 1989), in accordance with the principle of the duty of cooperation set out in Article 5 of the EEC Treaty, upon the courts of the Member States (see also the judgment of the Court of Justice in Case 177/78, Pigs and Bacon Commission v McCarren and Company Limited, judgment of 26 June 1979, opinion of Mr Advocate General Warner of 15 May 1979 on that case, his opinion in Case 33/76, REWE, of 30 November 1976 and his opinion in Case 74/76, lannelli & Volpi, of 10 February 1977).

The courts in the Member States may, in so far as Community law does not itself provide rules for these matters, uphold these claims only in accordance with their own procedural law, including the rules concerning admissibility, the prerequisites for bringing an action and the periods within which such actions must be brought. This is shown by a number of decisions given by the Court of Justice, of which only the following need be mentioned: Case 6/60, Jean-E. Humblet v Belgian State, judgment of 16 December 1960, [1960] ECR 559, Case 28/67 Firma Molkerei-Zentrale Westfalen/Lippe GmbH v Hauptzollamt Paderborn, judgment of 3 April 1968, [1968] ECR 143, Case 34/67, Firma Gebrüder Lück v Hauptzollamt Köln-Rheinau, judgment of 4 April 1968, [1968] ECR 245, Case 13/68 S.p.A., Salgoil v Italian Ministry for Foreign Trade, judgment of 19 December 1968, [1968] ECR 453), Case 120/73, Gebr. Lorenz GmbH v Federal Republic of Germany and the Land Rheinland/Pfalz, judgment of 11 December 1973 [1973] ECR 1471, Case 121/73, Markmann KG v Federal Republic of Germany and the Land Schleswig-Holstein, judgment of 11 December 1973, [1973] ECR 1495), Case 141/73, Fritz Lohrey v Federal Republic of Germany and the Land Hessen, judgment of 11 December 1973, [1973] ECR 1527, Case 33/76, REWE-Zentralfinanz eG and REWE-Zentral AG v Landwirtschaftskammer fur das Saarland and Case 45/76 Comet B.V. v Produktschap voor Siergewassen, judgment of 16 December 1976, [1976] ECR 2043.

It may also be inferred from these judgments that the fact that its application will differ in accordance with the varying national procedural rules is deliberately taken into account by Community law, which is not complete in this respect. This was pointed out by the Court of Justice particularly in Case 33/76 (REWE), when it stated that in the absence of measures of harmonization the rights conferred by Community law must be exercised before the national courts in accordance with the conditions laid down by national rules; the Court however placed the two reservations on this: the conditions imposed by domestic law must not, on the one hand, be less favourable than those relating to similar actions of a domestic nature and, on the other, the procedural conditions and time-limits must not make it impossible in practice to exercise the rights which the national courts are obliged to protect.

In my opinion these references to domestic law apply not only to procedural rules, but also to the conditions for entitlement to the rights afforded by Community law and to the repayment of interest, in so far as Community law contains no rules applicable in the matter. The Court of Justice also evidently assumes this reference to national substantive law when it ruled in Case 74/76 (Iannelli & Volpi) that “it is... for the national court within the framework of its own legal system to decide whether the whole of any internal taxation which is discriminatory within the meaning of Article 95 or only that part of it which exceeds the tax assessed on the domestic product is to be regarded as not payable”. The Court was even more precise in Case 177/78 (Pigs and Bacon) when it pointed out that it is for the national court to determine whether and to what extent a given levy must be reimbursed.

The domestic law applicable in this context also remains, however, subject to the limits imposed by Community law on procedural law mentioned already in Case 33/76 (REWE) and referred to above. As the Danish Government rightly points out these conditions are satisfied where the courts have developed their own legal concept of the claim to repayment, since that is also applicable first of all in respect of similar claims made under domestic law. Proof of damage or impoverishment as a precondition for bringing proceedings is known in the legal systems of all the Member States and in the Community legal system itself as an expression of the general principle of natural justice (see Case 90/78, Granaria B.V.v Council and Commission of the European Communities, judgment of 28 March 1979 and Joined Cases 83 and 94/76, 4, 15 and 40/77, Bayerische HNL Vermehrungsbetriebe GmbH & Co. KG and Others v Council and Commission of the European Communities, judgment of 25 May 1978 [1978] ECR 1209).

In my opinion it follows that in the present case the question of the repayment of taxes paid contrary to Article 95 should be settled according to Danish law. Concluding my examination, I may say that from the point of view of Community law claims by individuals for reimbursement of unlawfully levied taxes cannot be made to depend on whether a formal complaint has been lodged or whether legal proceedings have been instituted. The situation of bringing proceedings against Member States in the sphere of tax law cannot be compared with that in Case 43/75 (Gabrielle Defrenne v Société Anonyme Belge de Navigation Aérienne Sabena, judgment of 8 April 1976, [1976] ECR 455), in which the Court limited the retroactive effect of its judgment because a large number of persons, especially private employers, had gained a false impression of their duties owing to the conduct of the Community institutions and the governments of the Member States. In that case there was serious ground for fearing that many undertakings would incur financial difficulties if it were necessary to raise again the question of their conduct in matters which were already concluded.