Supremacy of EU law

Supremacy of EU law is the proposition that, where a valid rule of EU law conflicts with a rule of national law, the national rule must yield. It is better described as a doctrine of primacy than of hierarchy in the ordinary domestic sense. EU law does not repeal the inconsistent national measure; rather, the national court is required to disapply it so far as necessary to secure the effectiveness of EU law. The distinction matters. In Factortame, the Merchant Shipping Act 1988 remained an Act of Parliament, but it could not be applied against claimants whose directly effective Community rights it infringed.

For Part IB purposes the topic sits at the junction of EU constitutional law and UK constitutional law. From the Court of Justice’s perspective, supremacy was an inherent feature of the new legal order created by the Treaties. The point was first made in Costa v ENEL and then sharpened in Internationale Handelsgesellschaft and Simmenthal. From the United Kingdom perspective, supremacy was mediated by the European Communities Act 1972. The UK, as a dualist state, did not treat treaties as self-executing in domestic law. The ECA was therefore the statutory conduit through which directly effective EU rights became enforceable in UK courts. Section 2(4) supplied the interpretative and priority rule: future and past legislation was to be construed and have effect subject to section 2.

Three analytical distinctions should be kept clear. First, supremacy is not the same as direct effect. Direct effect concerns whether a provision of EU law is sufficiently capable of being invoked before a national court. Supremacy concerns what happens where such a provision conflicts with national law. Secondly, supremacy is not the same as consistent interpretation. The Marleasing duty requires national courts, so far as possible, to interpret domestic law consistently with EU law. Supremacy becomes decisive where interpretation cannot cure the inconsistency. Thirdly, supremacy should not be confused with validity. EU law did not render inconsistent Acts of Parliament void ab initio. It required disapplication for the purposes of deciding the case.

Brexit has altered the domestic significance of the doctrine without making it historically dispensable. The European Union (Withdrawal) Act 2018 preserved a transitional version of supremacy for pre-exit domestic law, so that retained EU law was not made incoherent overnight. The Retained EU Law (Revocation and Reform) Act 2023 has since moved UK law further away from the old priority structure, replacing much retained EU law with assimilated law and abolishing general supremacy after the end of 2023 subject to saving and restatement mechanisms. In an examination answer, however, it remains essential to understand the pre-Brexit doctrine: it explains Factortame, the architecture of the ECA, the constitutional status of EU law in the UK, and the continuing problems of retained or assimilated law.

The doctrine of supremacy was not expressed in clear terms in the original EEC Treaty. Its emergence was judicial. The Court of Justice reasoned from the special character of the Community legal order: Member States had conferred powers on common institutions, created rights for individuals, and accepted obligations intended to be uniformly applied. If national law could prevail whenever a national legislature chose, the Treaty system would be reduced to a set of ordinary international obligations. The Court therefore converted the structural premise of integration into a legal priority rule.

The first step was Van Gend en Loos. Although that case is usually classified under direct effect, it supplied the necessary constitutional premise: Community law was not merely a compact between states but a legal order capable of conferring rights on individuals. Costa v ENEL then answered the priority question. The Court held that the Treaty created an independent source of law which could not be overridden by later domestic legislation. That was a bold conclusion. In ordinary international law, a state may breach its obligations by enacting inconsistent legislation, but its domestic courts will apply domestic law unless the national constitution says otherwise. The Court of Justice insisted on a different model: the effectiveness and uniformity of Community law required domestic courts to give EU law priority.

The doctrine became more exacting in Internationale Handelsgesellschaft. The Court held that even national constitutional rules could not affect the validity or application of Community law. This was doctrinally necessary if primacy was to be uniform, but politically sensitive because it appeared to subordinate national constitutional identity to a legal order then lacking a mature bill of rights. The Court’s later development of general principles of EU fundamental rights was partly a response to this concern, particularly to resistance from constitutional courts such as the German Federal Constitutional Court.

Simmenthal completed the operational doctrine. It was not enough for national courts eventually to secure compliance through constitutional litigation or legislative amendment. Every national court seised of a case within its jurisdiction had to give full effect to directly applicable EU law and, where necessary, refuse to apply conflicting national legislation, even if that legislation was later in time. Supremacy therefore became a rule about ordinary adjudication, not only about inter-institutional relations.

The United Kingdom joined the Communities in 1973. The orthodox Diceyan account of parliamentary sovereignty presented an immediate problem: no Parliament can bind its successors, and courts must apply the latest inconsistent Act. The ECA 1972 managed that problem by a domestic technique. It incorporated directly effective EU law and instructed courts to construe and give effect to legislation subject to that incorporation. In Macarthys v Smith and Garland v British Rail, UK courts accepted strong interpretative duties. Factortame then showed the full consequence: an Act of Parliament could be disapplied where it conflicted with directly effective Community law.

The history should therefore be told as two connected narratives. At EU level, supremacy was articulated as an inherent constitutional attribute of the Union legal order. At UK level, supremacy operated because Parliament enacted the ECA and courts treated it as a constitutional statute which ordinary implied repeal could not silently undo. The tension between those accounts generated much of the academic debate and remains central to post-Brexit analysis.

The first principle is priority in case of conflict. If a national rule conflicts with a valid and applicable rule of EU law, the national court must give effect to EU law. The domestic rule is not necessarily invalid in the abstract; it is set aside to the extent of inconsistency. This remedial language of disapplication is preferable to saying that EU law repeals domestic law. In Factortame the Merchant Shipping Act 1988 did not disappear from the statute book. It could not be applied so as to defeat directly effective EU rights.

The second principle is uniformity. Supremacy exists because EU law would be ineffective if its effect depended on each Member State’s constitutional rules. A directive, regulation, Treaty article or general principle cannot mean one thing in one state and another thing in another because a domestic rule purports to prevail. The Court of Justice’s reasoning in Costa and Simmenthal is functional as well as constitutional: without priority, common obligations would fragment.

The third principle is comprehensiveness. From the EU perspective, supremacy extends over all forms of national law, including later legislation and constitutional norms. Internationale Handelsgesellschaft is the canonical statement. A Member State cannot invoke its constitution to defeat EU law. The point later appeared in cases concerning fundamental rights and constitutional identity, though modern EU law also contains Article 4(2) TEU, requiring respect for national identities inherent in fundamental political and constitutional structures. That provision qualifies the tone of the supremacy doctrine but does not abolish it. The ordinary rule remains that national courts cannot unilaterally give priority to domestic constitutional provisions over EU obligations.

The fourth principle is immediate judicial effect. Simmenthal requires national courts to set aside conflicting national rules without waiting for legislative repeal or constitutional adjudication by a higher court. This is important in problem questions. If a claimant invokes a directly effective Treaty provision against a public authority, the national court is not merely entitled but obliged to secure the EU right. That may require an interim remedy, as in Factortame, because the practical protection of the right would otherwise be lost before final judgment.

The landmark cases should be organised by function rather than memorised as a list. Van Gend en Loos supplies the foundation. The Court of Justice described the Community as a new legal order in which individuals could hold rights enforceable before national courts. Without that move, supremacy would have remained largely inter-state: national governments might owe obligations, but individuals could not easily insist on them in domestic litigation.

Costa v ENEL is the first clear supremacy case. The dispute itself concerned the nationalisation of electricity in Italy, but its constitutional significance lies in the Court’s insistence that later national legislation could not override Community law. The Court’s reasoning relied on the transfer of powers, the permanence of the limitation thereby accepted, and the need for uniform effectiveness. Costa should be treated as the doctrinal birth of primacy.

Internationale Handelsgesellschaft extends the doctrine to national constitutional law. The German claimant argued that Community measures conflicted with fundamental rights protected under the German Basic Law. The Court responded that the validity of Community measures could be judged only by Community law, not by national constitutional standards. The case is central because it shows the maximalist EU conception: supremacy applies even against constitutional rights. It also explains why the Court later developed general principles of fundamental rights as part of EU law.

Simmenthal is the operational masterpiece. It tells national courts what to do. They must give full effect to EU law and set aside conflicting national rules of their own motion where necessary. They need not await repeal by Parliament, annulment by a constitutional court, or any other domestic procedure. This made supremacy an everyday judicial duty.

Factortame translated these ideas into the United Kingdom constitution. Spanish-owned fishing companies challenged nationality requirements in the Merchant Shipping Act 1988. The House of Lords accepted that interim relief could be granted against the Crown and that a later Act of Parliament could be disapplied where it conflicted with directly effective Community rights. Its practical effect was dramatic: it displaced the traditional rule that courts could not suspend Acts of Parliament.

Thoburn and HS2 belong to the domestic constitutional afterlife of Factortame. Thoburn held that the ECA was a constitutional statute not subject to implied repeal. HS2 emphasised that the effect of EU law in the UK derived from the ECA and that some fundamental constitutional principles might not be overridden by general words. These cases do not erase Factortame; they domesticate it. They show UK courts explaining EU supremacy through constitutional statutes, parliamentary intention and the common law’s account of constitutional fundamentals.

A sophisticated answer also distinguishes supremacy from harmonisation. In Tobacco Advertising and later competence cases, the issue was whether the EU had power to legislate at all. Supremacy operates only if the EU measure is valid. A national court may question validity through Article 267 TFEU, but it cannot declare an EU act invalid on its own authority.

See practice questions section below.

See further reading section below.