Primacy of European Union law

In Costa v. ENEL.[7] Mr Costa was an Italian citizen opposed to the nationalisation of energy companies. Because he had shares in a private corporation subsumed by the nationalised company, ENEL, he refused to pay his electricity bill in protest. In the subsequent suit brought to Italian courts by ENEL, he argued that nationalisation infringed EC law on the state distorting the market.[8] The Italian government believed that not to be an issue that even could be complained about by a private individual since it was a decision to make by a national law. The ECJ ruled in favour of the government because the relevant treaty rule on an undistorted market was one on which the Commission alone could challenge the Italian government. As an individual, Mr Costa had no standing to challenge the decision, because that treaty provision had no direct effect.[9] But on the logically prior issue of Mr Costa's ability to raise a point of EC law against a national government in legal proceeding before the courts in that member state the ECJ disagreed with the Italian government. It ruled that EC law would not be effective if Mr Costa could not challenge national law on the basis of its alleged incompatibility with EC law.

It follows from all these observations that the law stemming from the treaty, an independent source of law, could not, because of its special and original nature, be overridden by domestic legal provisions, however framed, without being deprived of its character as community law and without the legal basis of the community itself being called into question.[10]

In other cases, state legislatures write the precedence of EU law into their constitutions. For example, the Constitution of Ireland contains this clause: "No provision of this Constitution invalidates laws enacted, acts done or measures adopted by the State which are necessitated by the obligations of membership of the European Union or of the Communities".

• C-106/77, Simmenthal [1978] ECR 629, duty to set aside provisions of national law that are incompatible with Union law.
• C-106/89 Marleasing [1991] ECR I-7321, national law must be interpreted and applied, if possible, to avoid a conflict with a Community rule.

Article I-6 of the European Constitution stated: "The Constitution and law adopted by the institutions of the Union in exercising competences conferred on it shall have primacy over the law of the Member States". The proposed constitution was never ratified, after being rejected in referendums in France and the Netherlands in 2005. Its replacement, the Treaty of Lisbon, did not include the article on primacy but instead included the following declaration:

17. Declaration concerning primacy
The Conference recalls that, in accordance with well settled case law of the Court of Justice of the European Union, the Treaties and the law adopted by the Union on the basis of the Treaties have primacy over the law of Member States, under the conditions laid down by the said case law.
The Conference also decided to attach as an Annex to this Final Act the Opinion of the Council Legal Service on the primacy of EC law as set out in 11197/07 (JUR 260):

Opinion of the Council Legal Service
of 22 June 2007
It results from the case-law of the Court of Justice that primacy of EU law is a cornerstone principle of Union law. According to the Court, this principle is inherent to the specific nature of the European Community. At the time of the first judgment of this established case law (Costa/ENEL,15 July 1964, Case 6/641 (¹) there was no mention of primacy in the treaty. It is still the case today. The fact that the principle of primacy will not be included in the future treaty shall not in any way change the existence of the principle and the existing case-law of the Court of Justice.

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(¹) It follows (...) that the law stemming from the treaty, an independent source of law, could not, because of its special and original nature, be overridden by domestic legal provisions, however framed, without being deprived of its character as Community law and without the legal basis of the Community itself being called into question.

— Declaration 17, Consolidated EU Treaties[11]

Depending on the constitutional tradition of member states, different solutions have been developed to adapt questions of incompatibility between State law and Union law to one another. EU law is accepted as having supremacy over the law of member states, but not all member states share the ECJ's analysis on why EU law takes precedence over state law if there is a conflict.

The United Kingdom was a member state of the European Union and its predecessor the European Communities from 1 January 1973 until 31 January 2020. During this time the issue of EU law taking precedence over national law was a significant issue and a cause for debate both among politicians and even in the judiciary.

In R v Secretary of State for Transport, ex p Factortame Ltd, the House of Lords ruled that courts in the United Kingdom had the power to "disapply" acts of parliament if they conflicted with EU law. Lord Bridge held that Parliament had voluntarily accepted this limitation of its sovereignty and was fully aware that even if the limitation of sovereignty was not inherent in the Treaty of Rome, it had been well established by jurisprudence before Parliament passed the European Communities Act 1972.[22]

If the supremacy within the European Community of Community Law over the national law of member states was not always inherent in the EEC Treaty it was certainly well established in the jurisprudence of the Court of Justice long before the United Kingdom joined the Community. Thus, whatever limitation of its sovereignty Parliament accepted when it enacted the European Communities Act 1972 was entirely voluntary. Under the terms of the 1972 Act it has always been clear that it was the duty of a United Kingdom court, when delivering final judgment, to override any rule of national law found to be in conflict with any directly enforceable rule of Community law.

In 2011 the UK Government, as part of the Conservative–Liberal Democrat coalition agreement following the 2010 UK general election, passed the European Union Act 2011 in an attempt to address the issue by inserting a sovereignty clause.[23] The clause was enacted in section 18 which says:

Directly applicable or directly effective EU law (that is, the rights, powers, liabilities, obligations, restrictions, remedies and procedures referred to in section 2(1) of the European Communities Act 1972) falls to be recognised and available in law in the United Kingdom only by virtue of that Act or where it is required to be recognised and available in law by virtue of any other Act.

However, in the 2014 case of R (HS2 Action Alliance Ltd) v Secretary of State for Transport, the Supreme Court of the United Kingdom said:[24][25]

The United Kingdom has no written constitution, but we have a number of constitutional instruments. They include Magna Carta, the Petition of Right 1628, the Bill of Rights and (in Scotland) the Claim of Rights Act 1689, the Act of Settlement 1701 and the Act of Union 1707. The European Communities Act 1972, the Human Rights Act 1998 and the Constitutional Reform Act 2005 may now be added to this list. The common law itself also recognises certain principles as fundamental to the rule of law. It is, putting the point at its lowest, certainly arguable (and it is for United Kingdom law and courts to determine) that there may be fundamental principles, whether contained in other constitutional instruments or recognised at common law, of which Parliament when it enacted the European Communities Act 1972 did not either contemplate or authorise the abrogation.

At 23:00 GMT (00:00 CET in Brussels) on 31 January 2020, after 47 years of membership, the United Kingdom became the first member state to formally leave the European Union. It did so under the terms of the Brexit withdrawal agreement. At the same time, the European Communities Act 1972 (ECA 1972), the piece of legislation that incorporated EU law (Community law as it was in 1972) into the domestic law of the United Kingdom, was repealed by the European Union (Withdrawal) Act 2018, although the effect of the 1972 Act was saved by the provisions of the European Union (Withdrawal Agreement) Act 2020 to enable EU law to continue to have legal effect within the UK until the end of the implementation period, which ended on 31 December 2020. Since the implementation period has now ended, EU law no longer applies to the UK. However the principle of the supremacy of EU law applies to the interpretation of retained EU law.[26]

In September 2021 the UK government announced a review of retained EU law, aiming to remove the special status retained European Union law currently holds in the United Kingdom, and to repeal retained EU laws which are "no longer right for the UK".[27] The Retained EU Law (Revocation and Reform) Act 2023 became law in June 2023, the act allows the UK government to revoke retained EU laws, modify those remaining and changes how such laws are interpreted. The original act aimed to revoke over 4000 laws by the end of 2023, however this was later reduced to 800, with the remaining laws still under review.

• Thoburn v Sunderland City Council (2002)
• Van Gend en Loos v Nederlandse Administratie der Belastingen (1963)
• National Identity Clause
• Supremacy Clause, analogous concept within the Constitution of the United States
• Section 109 of the Constitution of Australia – analogous concept within the Constitution of Australia
• Paramountcy (Canada) – analogous doctrine in Canadian constitutional law