Supremacy of EU law

Supremacy is the proposition that, where a valid rule of EU law conflicts with a rule of national law, the EU rule prevails. In orthodox EU doctrine it is not merely a rule of interpretation. It requires the national court to secure the full effectiveness of EU law, if necessary by setting aside the inconsistent domestic measure. That is why the subject belongs at the beginning of EU Constitutional Law. Week 1 identified the sources and institutions of EU law; Week 2 asks how those sources operate in a domestic legal order which also claims constitutional authority.

The doctrine was made by the Court of Justice rather than by express Treaty text. The Treaty of Rome did not state in terms that Community law was supreme over national law. The Court nevertheless reasoned, beginning with Van Gend en Loos and Costa v ENEL, that the Treaties created a new legal order, that Member States had limited their sovereign rights in the fields covered by the Treaties, and that the uniformity and effectiveness of Community law would be destroyed if later national legislation could prevail. Supremacy was therefore presented as a structural implication of membership.

For English lawyers the point is more difficult. The traditional doctrine of parliamentary sovereignty says that Parliament may make or unmake any law, and that no court may question the validity of an Act of Parliament. EU supremacy, by contrast, required domestic courts to refuse to apply inconsistent Acts of Parliament within the scope of EU law. The reconciliation adopted in the United Kingdom was statutory rather than revolutionary. Section 2(1) of the European Communities Act 1972 incorporated directly effective EU rights into domestic law; section 2(4) required legislation to be construed and have effect subject to that incorporation. Factortame then demonstrated the consequence: even primary legislation could be disapplied where it conflicted with directly effective EU law.

For Durham first-year purposes, three distinctions are essential. First, supremacy is not the same as direct effect. Direct effect asks whether a provision of EU law is capable of being invoked by a party before a national court. Supremacy asks what happens if that applicable EU rule conflicts with national law. Secondly, supremacy is not the same as direct applicability. Regulations are directly applicable under Article 288 TFEU, but supremacy may be engaged by Treaty provisions, regulations, decisions, and sufficiently precise provisions of directives, subject to the limits on horizontal direct effect of directives. Thirdly, disapplication is not invalidation. A domestic rule which conflicts with EU law is normally not struck from the statute book; it is left unapplied to the extent of the incompatibility.

Brexit changes the domestic foundation, but it has not made the topic obsolete. First, the classical cases remain examined because they explain the constitutional relationship between EU law and national law. Secondly, pre-exit and transition-period disputes may still arise. Thirdly, retained EU law, now largely renamed assimilated law, requires understanding of how supremacy was saved, limited, and then largely ended by legislation. Fourthly, the topic supplies a central comparison for UK constitutional law: Parliament can authorise a priority rule, and Parliament can later withdraw or reshape it. The best examination answers therefore do not recite Costa and Factortame as isolated monuments. They explain the different constitutional perspectives from Luxembourg and Westminster, and they show how the UK courts translated EU supremacy into domestic legal technique.

The historical development of supremacy has two overlapping stories: the internal constitutionalisation of the European Community, and the reception of that doctrine by national constitutional systems. The first story begins in the 1960s. The early Community had limited express competences, but it also had institutions empowered to make binding law and a Court charged with ensuring that the law was observed. If each Member State could give priority to later national legislation, Community obligations would become contingent upon domestic political will. The Court of Justice therefore developed principles which converted the Treaties from ordinary international obligations into a constitutional legal order.

Van Gend en Loos established direct effect. The Court held that Treaty provisions could confer rights on individuals enforceable before national courts. That was decisive: if individuals were to rely upon Community law domestically, national courts had to know what to do when domestic law pointed in the opposite direction. Costa v ENEL supplied the answer. The Court reasoned that the Member States had created a Community of unlimited duration, with its own institutions, personality, legal capacity, and powers stemming from a limitation of sovereignty. The consequence was that national law could not override Community law without undermining the Community itself.

The doctrine then hardened. Internationale Handelsgesellschaft held that the validity of Community measures could not be judged by national constitutional standards, including fundamental rights protected by a domestic constitution. Simmenthal required every national court to apply Community law in full and to set aside conflicting national measures, including later legislation, without waiting for legislative repeal or constitutional review. These decisions are important because they show that supremacy was conceived in Luxembourg as an unconditional rule internal to the EU legal order. The duty was judicial, immediate, and general.

The second story concerns national reception. Member States did not all accept the Court’s doctrine on the same theoretical basis. Some constitutional courts accepted primacy subject to reservations protecting constitutional identity, fundamental rights, or the limits of EU competences. The German Federal Constitutional Court’s Solange and Maastricht lines of authority are the most famous examples. The United Kingdom’s position was distinctive because it lacked a codified constitution and because parliamentary sovereignty was the central organising doctrine.

When the UK joined the Communities in 1973, the European Communities Act 1972 provided the domestic gateway. It was not framed as a constitutional surrender in the language of the Court of Justice. It was an Act of Parliament which gave effect to enforceable Community rights and required inconsistent domestic law to yield. That made the UK position both orthodox and unstable. It was orthodox because domestic judges could say that they were obeying Parliament: Parliament had instructed them, through the 1972 Act, to give legal effect to Community law. It was unstable because the instruction appeared to require courts to disapply later Acts of Parliament, something which orthodox Diceyan theory had treated as impossible.

Factortame exposed the tension. The Merchant Shipping Act 1988 sought to restrict registration of fishing vessels. Spanish-owned companies alleged that the legislation breached EU law, including rights against discrimination and restrictions on establishment. The House of Lords granted interim relief disapplying the Act pending a ruling from the Court of Justice. That was the first unmistakable modern instance in which UK courts refused to apply an Act of Parliament because of EU law. Lord Bridge emphasised that this was not an unforeseen judicial coup: Parliament had voluntarily accepted this consequence by enacting the 1972 Act.

Later cases refined the domestic explanation. In Thoburn, Laws LJ described the 1972 Act as a constitutional statute which could not be impliedly repealed. In HS2, the Supreme Court suggested that even EU law’s domestic effect depended upon fundamental constitutional principles of UK law. Miller confirmed that EU law was a source of domestic law only because Parliament had made it so through the 1972 Act. Brexit then removed that gateway. The European Union (Withdrawal) Act 2018 repealed the 1972 Act, preserved and converted much EU-derived law, and initially saved a limited form of supremacy for pre-exit domestic legislation. The Retained EU Law (Revocation and Reform) Act 2023 then abolished the general domestic principle of supremacy from the end of 2023. Historically, therefore, supremacy in UK law is best understood as a powerful but statutorily mediated priority rule: created by EU constitutional doctrine, received through the 1972 Act, and reshaped by post-Brexit legislation.

The first principle is priority. Supremacy means that a valid and applicable EU norm prevails over inconsistent national law. The inconsistency may be direct, as where a national statute imposes a condition prohibited by EU law, or indirect, as where national procedural rules make EU rights practically impossible or excessively difficult to enforce. The remedy is usually disapplication of the inconsistent domestic rule in the case before the court. The national rule is not necessarily void for all purposes. It remains part of domestic law unless repealed or amended, but it cannot be applied so far as it conflicts with the EU obligation.

The second principle is effectiveness. The Court of Justice repeatedly links supremacy to effet utile: EU law must be effective and uniform across the Member States. If a Member State could rely upon its constitution, later statutes, administrative practice, or judicial procedure to defeat EU law, the same EU right would have different force in different states. Supremacy is therefore connected to equality between Member States and to the rule of law within the Union. A Member State may not plead domestic law as a justification for non-performance of EU obligations.

The third principle is breadth. In the classical EU account, supremacy extends over all forms of national law, including constitutional provisions. Internationale Handelsgesellschaft is the leading authority for the proposition that the validity of EU measures cannot be tested by national constitutional law. That does not mean the Court of Justice is indifferent to rights. It developed fundamental rights as general principles of EU law, drawing inspiration from common constitutional traditions and the European Convention on Human Rights. But the decisive point is institutional: the standard of review is an EU standard, not a national one.

The fourth principle is immediacy. Simmenthal requires ordinary national courts to give immediate effect to EU law without waiting for domestic legislative amendment, constitutional review, or authorisation by a higher national court. That is a strong judicial duty. It means that every national court within its jurisdiction must protect EU rights. The logic is not merely that EU law is relevant evidence of interpretation; it is that the inconsistent national rule must be put aside.

The case law should be learned as a sequence rather than as a list. Van Gend en Loos comes first because supremacy presupposes an EU norm capable of enforcement in national courts. The Court’s creation of direct effect transformed the individual from an object of international arrangements into a litigant able to rely on EU law. Once that move was made, the question of priority became unavoidable.

Costa v ENEL is the foundational supremacy case. The dispute itself was modest: a shareholder resisted an electricity bill after the nationalisation of the Italian electricity industry. The constitutional proposition was not modest. The Court held that Community law could not be overridden by domestic legal provisions without being deprived of its character as Community law. The reasoning is institutional and teleological: the Treaties established an autonomous legal order, and the obligations undertaken by Member States would be conditional and unequal if unilateral national measures could prevail.

Internationale Handelsgesellschaft extended the principle to national constitutional law. The German court was concerned with constitutional rights. The Court of Justice held that the validity of Community measures could not be affected by allegations that they conflicted with national constitutional principles. This is the high-water mark of the EU claim: primacy applies even against constitutional norms. The practical political response was the development of EU fundamental rights doctrine, but the formal hierarchy asserted by Luxembourg remained intact.

Simmenthal supplied the judicial machinery. A national court must apply EU law in full and set aside conflicting national law, whether earlier or later, without awaiting repeal or constitutional adjudication. This is why supremacy is sometimes described as decentralised constitutional review. Ordinary courts become EU courts for the purpose of securing effective EU law.

Factortame is the decisive UK authority. The House of Lords accepted that interim relief could be granted against the operation of an Act of Parliament where EU law required it. The case is sometimes overdramatised as the death of parliamentary sovereignty. That is imprecise. The better view is that Parliament, through the 1972 Act, had authorised a priority rule for EU law. The courts enforced that rule. Nevertheless, the symbolic importance is immense: an Act of Parliament was not applied because it conflicted with directly effective EU rights.

Thoburn reframed the issue in domestic constitutional language. Laws LJ held that the 1972 Act was a constitutional statute and therefore not subject to implied repeal. This allowed courts to explain why later ordinary statutes did not silently override EU rights. It also implied a hierarchy among statutes, not in the sense that Parliament could never repeal a constitutional statute, but in the sense that repeal had to be express or exceptionally clear.

HS2 and Miller add the modern constitutional qualification. HS2 suggested that the domestic effect of EU law depends on the constitutional instrument through which it is received, and that fundamental constitutional principles may condition that reception. Miller confirmed that EU law was an independent and overriding source of domestic law only because the 1972 Act made it so, and that removing that source required parliamentary authorisation. Together, these cases show that supremacy was both real in its practical effect and domestically contingent in its constitutional basis.

See practice questions section below.

See further reading section below.