Introduction
The principle of the supremacy of European Union (EU) law, established by the European Court of Justice (ECJ) in cases such as Costa v ENEL (1964), asserts that EU law takes precedence over conflicting national laws of Member States. This principle has historically posed significant challenges for dualist states like the United Kingdom (UK), where international law requires domestic incorporation to have effect. In contrast, monist states, such as Italy and France, embed international law directly into their legal systems. This essay explores the tension between EU law supremacy and national sovereignty in the UK as a dualist state, particularly through key legislative developments and landmark cases. It also briefly contrasts the UK’s experience with other dualist and monist states to highlight varying approaches to EU law integration. The analysis focuses on the period from the UK’s entry into the European Economic Community (EEC) in 1972 to its exit from the EU in 2020 (Brexit), evaluating how parliamentary sovereignty was both limited and ultimately restored. By examining critical judicial decisions and legislative milestones, this essay aims to demonstrate the complex interplay between EU law and national legal traditions.
The UK’s Dualist Framework and the Incorporation of EU Law
As a dualist state, the UK traditionally views international law and domestic law as separate legal orders. International obligations, such as treaties, do not automatically become part of domestic law unless incorporated through an Act of Parliament (Craig and de Búrca, 2020). This principle was fundamentally tested with the UK’s accession to the EEC in 1972 through the European Communities Act (ECA). Section 2(1) of the ECA provided for the direct effect of EU law within the UK legal system, while Section 2(4) mandated that UK legislation must be interpreted in line with EU law. This marked the beginning of a significant tension with the doctrine of parliamentary sovereignty—the idea that Parliament can make or repeal any law without restriction, as articulated by A.V. Dicey.
The tension became evident in early judicial interpretations. In the 1974 case of McCarthy v Smith, Lord Denning acknowledged that the UK had voluntarily limited its sovereignty by joining the EEC. However, he also maintained that Parliament retained the power to repeal the ECA, thereby reclaiming full sovereignty if it so desired (Loveland, 2021). This perspective highlighted a conditional acceptance of EU law supremacy, rooted in the UK’s dualist tradition, where ultimate authority remained with Parliament. Nevertheless, the practical implications of EU membership began to challenge this theoretical sovereignty.
Landmark Cases: Factortame and Thoburn
A turning point in the UK’s relationship with EU law supremacy came with the Factortame litigation in 1990. In this case, the ECJ ruled that national courts must disapply domestic legislation conflicting with EU law, even if the conflicting law was an Act of Parliament. Furthermore, the House of Lords granted an injunction against the Crown—an unprecedented move—prioritising EU law over the Merchant Shipping Act 1988 (Craig, 2018). The Factortame decision demonstrated that EU law could override parliamentary sovereignty in practice, even if, in theory, Parliament retained the power to repeal the ECA. This ruling arguably marked the high watermark of EU law supremacy in the UK.
The 2002 case of Thoburn v Sunderland City Council, commonly known as the Metric Martyrs case, further entrenched this dynamic. Lord Justice Laws classified the ECA as a “constitutional statute,” suggesting it was not subject to implied repeal by subsequent legislation. This decision confirmed the entrenched supremacy of EU law within the UK system, as long as the ECA remained in force (Elliott, 2002). However, it also reaffirmed the dualist stance that Parliament could explicitly repeal the ECA, maintaining a delicate balance between EU obligations and national sovereignty.
Brexit and the Restoration of Parliamentary Sovereignty
The 2016 Brexit referendum, in which 51.9% of UK voters opted to leave the EU, represented a decisive shift in the relationship between EU law and national sovereignty. The subsequent legal and political processes underscored the complexities of disentangling EU law supremacy from the UK system. In the 2017 case of R (Miller) v Secretary of State for Exiting the European Union (Miller No.1), the Supreme Court ruled that parliamentary approval was required to trigger Article 50 of the Treaty on European Union, reinforcing the primacy of parliamentary sovereignty in major constitutional decisions (Barber et al., 2017).
The European Union (Withdrawal) Act 2018 marked the formal end of EU law supremacy in the UK. Section 5 of the Act explicitly repealed the ECA and terminated the principle of EU law precedence after the UK’s exit on 31 January 2020. While the UK-EU Trade and Cooperation Agreement (TCA) preserved some economic links, it did not reinstate EU law supremacy, thereby restoring full parliamentary sovereignty (Barnard, 2021). Indeed, Brexit can be seen as the ultimate assertion of the UK’s dualist nature, prioritising national law over international obligations.
Comparative Perspectives: Dualist and Monist States
In contrast to the UK, other dualist states like Germany and Hungary have also grappled with EU law supremacy, often asserting national constitutional limits. For instance, in Germany’s Solange I (1974) decision, the Federal Constitutional Court prioritised the German Constitution over EU law unless the latter adequately protected human rights (Craig and de Búrca, 2020). Similarly, Hungary’s Constitutional Court in 2021 avoided applying EU law supremacy in asylum disputes, reflecting a broader trend of resistance amid rule of law concerns (Kelemen, 2022). These examples suggest that dualist states frequently seek to protect national sovereignty, much like the UK pre-Brexit.
Conversely, monist states such as Italy and France have generally integrated EU law more seamlessly. Italy’s Article 11 of its Constitution explicitly permits limitations on sovereignty for international cooperation, while France’s Article 55 accords treaties precedence over national laws (Craig, 2018). However, even in these states, conflicts arise—Italy’s Taricco II (2017) ruling prioritised national constitutional principles over EU law, marking a rare instance of domestic law prevailing. This indicates that, despite their monist frameworks, national identity and rights can still challenge EU law supremacy.
Conclusion
The principle of EU law supremacy has profoundly shaped the UK’s legal landscape as a dualist state, creating a persistent tension with parliamentary sovereignty from the enactment of the ECA in 1972 to Brexit in 2020. Landmark cases like Factortame and Thoburn demonstrated the practical dominance of EU law, while the Brexit process—culminating in the Withdrawal Act 2018—ultimately restored national legislative autonomy. Comparative analysis with other dualist and monist states reveals a spectrum of approaches to EU law integration, with resistance often emerging from constitutional or sovereignty concerns, as seen in Germany and Hungary. The UK’s experience, therefore, reflects a broader struggle within the EU to balance supranational authority with national legal traditions. Post-Brexit, the restoration of parliamentary sovereignty arguably reaffirms the dualist framework, though future trade and cooperation agreements may yet influence the UK’s legal autonomy. This dynamic underscores the enduring complexity of reconciling international obligations with domestic constitutional principles.
References
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- Barnard, C. (2021) The Substantive Law of the EU: The Four Freedoms. 7th edn. Oxford University Press.
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- Craig, P. and de Búrca, G. (2020) EU Law: Text, Cases, and Materials. 7th edn. Oxford University Press.
- Elliott, M. (2002) ‘Parliamentary Sovereignty and the New Constitutional Order: Legislative Freedom, Political Reality and Convention,’ Legal Studies, 22(3), pp. 340–376.
- Kelemen, R.D. (2022) ‘The European Union’s Authoritarian Equilibrium,’ Journal of European Public Policy, 29(4), pp. 481–499.
- Loveland, I. (2021) Constitutional Law, Administrative Law, and Human Rights: A Critical Introduction. 9th edn. Oxford University Press.
