PastPaperHero | Retained EU law and the UK constitution - Parliamentary sovereignty and retained EU law

Learning Outcomes

This article examines the relationship between parliamentary sovereignty, a core constitutional doctrine in the UK, and retained European Union (EU) law following Brexit, including:

The historical and current status of parliamentary sovereignty, including its theoretical and legal dimensions within the UK's uncodified constitution.
The mechanisms by which EU law attained supremacy in the UK legal order, especially through the European Communities Act 1972 (ECA 1972) and CJEU jurisprudence, and the limitations on traditional sovereignty through direct and indirect effect.
The legal effects of Brexit under the European Union (Withdrawal) Act 2018 (EU(WA) 2018): the transition from EU law to retained EU law, the altered operation (and limits) of the supremacy principle, and the practical operation of retained EU law within the domestic legal system.
UK courts’ interpretation and application of retained EU law, including the position regarding CJEU case law pre- and post-IP completion day, and the use of general principles in interpreting that law.
The implications for Parliament’s ability to legislate contrary to retained EU law, the principle of constitutional statutes, and the consequences for legal certainty and the role of the courts.
The methods by which EU-derived law can be amended, repealed, or otherwise modified by Parliament or through delegated powers, including the operation of Henry VIII clauses.

SQE1 Syllabus

For SQE1, you are required to understand the relationship between parliamentary sovereignty and retained EU law in the UK constitution, with a focus on the following syllabus points:

the sources and legal status of retained EU law following the UK's withdrawal from the EU
the principle of parliamentary sovereignty and the historical challenges posed by EU law and retained EU law
the interpretation and application of retained EU law, including the binding effect of CJEU decisions and the role of the higher UK courts
the constitutional relationship between retained EU law and statutes passed before and after IP completion day
the effect and significance of key legislation, most notably the European Union (Withdrawal) Act 2018 and the Retained EU Law (Revocation and Reform) Act 2023
the doctrine of constitutional statutes and relevant jurisprudence that inform the contemporary understanding of legislative hierarchy, repeal, and constitutional change

Test Your Knowledge

Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, remember to look more closely at that area during your revision.

Which Act provided the primary legal basis for incorporating EU law into the UK legal system prior to Brexit?
1. Human Rights Act 1998
2. European Union (Withdrawal) Act 2018
3. European Communities Act 1972
4. Bill of Rights 1689
What is the general principle established in R v Secretary of State for Transport, ex parte Factortame Ltd (No 2) regarding the relationship between EU law and UK statutes during the UK's EU membership?
1. UK statutes always prevail over conflicting EU law.
2. EU law could be disapplied by UK courts if it conflicted with fundamental UK constitutional principles.
3. UK courts had the power to suspend the application of UK statutes that conflicted with directly effective EU law.
4. The European Court of Justice had no jurisdiction over UK statutes.
According to the European Union (Withdrawal) Act 2018, what is the status of the principle of supremacy of EU law in relation to UK laws made after IP completion day (31 December 2020)?
1. Retained EU law continues to be supreme over all UK law.
2. The principle of supremacy no longer applies to laws made after IP completion day.
3. The principle of supremacy applies only if Parliament expressly states it should.
4. Retained EU law is supreme only if it relates to fundamental rights.

Introduction

The relationship between the UK's constitutional system, parliamentary sovereignty, and the evolving nature of European Union law present ongoing challenges in constitutional and administrative law. The UK’s unwritten constitution positions Parliament as the supreme law-making authority, yet membership of the EU and the subsequent absorption of EU law into the domestic system complicated this claim, as did the mechanism of withdrawal following the 2016 referendum (“Brexit”). The implementation of the European Communities Act 1972 (ECA 1972) entrenched the supremacy of EU law in the domestic hierarchy, challenging Parliament’s theoretical omnipotence. Brexit, achieved through the European Union (Withdrawal) Act 2018 (EU(WA) 2018), repealed ECA 1972 and replaced much of EU law with the new category of retained EU law. This article examines the continuing relevance of retained EU law, its status vis-à-vis parliamentary sovereignty, and the constitutional framework that now applies in post-Brexit Britain.

Parliamentary Sovereignty Before and During EU Membership

Key Term: parliamentary sovereignty
The constitutional principle that Parliament is the supreme legal authority in the UK, able to make or unmake any law, with no other body recognised by UK law as able to override or set aside its legislation.

A.V. Dicey's formulation of parliamentary sovereignty, which remains central to constitutional thought, affirms that Parliament may legislate on any subject, cannot bind future Parliaments, and is not subject to challenge by any court or other body. This positivist and “continuing” view was historically accepted by courts, barring scrutiny of both the substance and the procedure by which Acts were passed.

Parliament’s legislative authority is not subject to higher constitutional law or entrenched statutes. Changes to significant constitutional matters, such as the franchise, the structure of government, or fundamental rights, have all been made by simple majorities in Parliament—often with limited or no additional procedural requirements.

However, real-world political constraints—including public opinion, established constitutional conventions, and political morality—have always qualified Parliament’s legal freedom of action. Legal limitations, however, were rare outside of express repeal or amendment by Parliament itself.

Acts of Parliament and the Hierarchy of Law

Acts of Parliament are at the apex of the UK legal hierarchy. Even constitutional statutes, such as the Magna Carta, Bill of Rights 1689, Acts of Union 1707, and Human Rights Act 1998, are subject to amendment or repeal by ordinary legislative process. Only in very limited and exceptional cases—arguably, those relating to the fundamental terms of union or political settlement—has Parliament’s absolute legislative freedom been questioned.

Judicial review of primary legislation is not generally permitted in the UK legal system, reaffirmed by decisions such as Pickin v British Railways Board [1974] AC 765 and R (Jackson) v Attorney General [2005] UKHL 56. Even when Parliament acts contrary to international law, treaty obligations, or established conventions, the courts will apply the clear terms of an Act of Parliament.

International Law, Conventions, and Treaties

Where international treaties require the creation of domestic legal rights or obligations (such as the EU Treaties), UK constitutional law has required this to be achieved by statute, not simply by executive act. The dualist tradition means international obligations do not automatically have legal effect unless enacted by Parliament.

The European Communities Act 1972 and the Challenge to Sovereignty

With accession to the European Communities, Parliament enacted the ECA 1972. This was not merely an ordinary statute: it was the gateway by which directly effective EU law entered the UK legal order and set the terms for the relationship between domestic law and EU obligations.

Section 2(1) gives direct effect to those rights, obligations, and remedies created by the EU Treaties and directly applicable measures, requiring UK courts to give legal effect to these provisions without further enactment.
Section 2(4) provides that any domestic legislation (past or future) “shall be construed and have effect subject to” directly applicable rights and obligations, requiring UK courts to interpret national law in line with EU law and, where impossible, to set aside conflicting domestic law.

While, in a sense, Parliament remained formally sovereign—it could, in principle, repeal the ECA 1972—it had, and did, restrict its own legislative options as long as the Act was in force.

Supremacy of EU Law: Factortame and its Legacy

The principle of the supremacy of EU law is perhaps most dramatically reflected in the litigation surrounding R v Secretary of State for Transport, ex parte Factortame Ltd (No 2) [1991] 1 AC 603. The House of Lords accepted that, by passing the ECA 1972, Parliament had for so long as that Act remained in force “voluntarily limited its own sovereignty” by giving UK courts a clear duty to disapply conflicting UK statutes in favour of directly effective EU norms.

Factortame and similar decisions marked a practical, if not theoretical, limitation on parliamentary sovereignty: UK courts could (and indeed were required to) deny effect to a UK Act if it clashed irreconcilably with EU law, thanks to the clear wording and intention of the ECA 1972 and the supremacy doctrine established in CJEU jurisprudence, especially Costa v ENEL [1964] ECR 585 and Internationale Handelsgesellschaft.

A further consequence was that parliamentary sovereignty was modified by the ongoing power of Parliament to repeal the ECA 1972 (which it eventually did)—but, so long as the Act persisted, the “supremacy” of EU law was a real and binding feature of the constitutional order.

Worked Example 1.1

A UK Act of Parliament enacted in 1988 restricts certain activities which conflict, on their face, with an EU Regulation with direct effect. A question arises in the High Court as to which should prevail.

Answer:
The court must give effect to the directly effective EU Regulation due to s 2(4) ECA 1972, and following Factortame, has the power to disapply the UK Act insofar as it conflicts with the EU Regulation.

Constitutional Statutes and Implied Repeal

The judiciary, in decisions such as Thoburn v Sunderland City Council [2002] EWHC 195 (Admin), signalled that certain “constitutional statutes” (including the ECA 1972, Magna Carta 1215, the Bill of Rights 1689, the Human Rights Act 1998, and the devolution statutes) enjoy protection from implied repeal. This means that any amendment or repeal of such statutes must be by express provision, not mere inconsistency with a later Act. However, even “constitutional statutes” can be expressly repealed or amended by Parliament, and the doctrine creates a hierarchy of sorts but does not create entrenched, unchangeable laws.

Key Term: constitutional statutes
Statutes with significant constitutional importance, which according to some judicial statements, may only be amended or repealed by express words, not by implication, though Parliament may still ultimately legislate contrary to them.

Nonetheless, the prevailing orthodoxy remains that Parliament is not legally fettered in its ability to expressly repeal or alter even the most entrenched constitutional statutes.

Retained EU Law and Sovereignty Post-Brexit

After the referendum to leave the EU, the UK repealed the ECA 1972 with effect from 'exit day'—31 January 2020—using the EU(WA) 2018. To ensure legal continuity and avoid a legislative vacuum, the EU(WA) 2018 converted relevant EU law and implemented provisions into the new category of 'retained EU law'.

Key Term: retained EU law
Law which formed part of the UK legal system immediately before IP completion day as a result of EU membership and which continues to have effect domestically pursuant to the EU(WA) 2018.

Retained EU law is made up primarily of the following:

EU-derived domestic legislation (s 2): UK statutes and statutory instruments made to comply with EU obligations, especially those made to implement directives.
- Remains as primary or secondary legislation, retaining its pre-exit status.
- Examples: UK statutory instruments implementing EU employment, health and safety, or consumer protection directives.
Direct EU legislation (s 3): EU regulations and decisions which were directly applicable in the UK (without national implementing act).
- Classified as retained direct principal EU legislation (e.g., most EU regulations) or minor EU legislation (e.g., some implementing decisions).
Rights, liabilities, etc. saved by s 4: This covers directly effective rights arising from the EU Treaties or directives recognised by the courts as enforceable prior to IP completion day.
Retained EU case law and general principles of EU law (ss 5-6): Pre-IP completion day CJEU case law and recognised general principles are retained where relevant to interpretation of retained EU law.

Section 1 repealed ECA 1972 but, crucially, this was not an automatic "wipe" of all EU law—rather, it was a complex legal "snapshot" of the status quo, preserving most directly effective EU law at IP completion day unless and until amended by subsequent legislation.

Categories and Status of Retained EU Law

Retained EU law is not a single class. Its origins affect its status:
- EU-derived domestic law continues as either primary or secondary legislation; its status is unchanged.
- Retained direct EU legislation (e.g., most regulations) does not map neatly onto traditional categories and, for specific purposes (such as the Human Rights Act 1998), is treated as primary legislation (if principal) or secondary (if minor).
- Retained directly effective rights, such as Art 157 TFEU (equal pay), retain their status as part of UK domestic law but are no longer enforced as "EU" rights.

Supremacy and Parliamentary Sovereignty in the Retained EU Law Framework

Section 5(1) of EU(WA) 2018 provides that the principle of the supremacy of EU law does not apply to any enactment or rule of law made on or after IP completion day (31 December 2020). This means full parliamentary sovereignty is restored for future legislation—Parliament may enact whatever it wishes, including provisions expressly contradicting retained EU law.

However, s 5(2) provides that, for legislation made or passed before IP completion day, retained EU law retains its supremacy as against pre-IP completion day enactments, unless Parliament expressly legislates otherwise. The upshot:

Retained EU law will prevail over conflicting domestic law made before IP completion day, unless Parliament subsequently amends or repeals it.
Acts of Parliament after IP completion day take precedence over retained EU law, affirming the restored principle of parliamentary sovereignty.

Worked Example 1.2

An EU Regulation in force in 2017 (relating to food safety) became retained EU law. A UK Act, passed in 2014, contains conflicting requirements. In 2023, a regulatory dispute arises.

Answer:
The retained EU Regulation, under s 3, retains its supremacy over pre-IP completion day legislation, so it prevails over the 2014 Act for events occurring after IP completion day, unless the UK Parliament amends the position.

Worked Example 1.3

Suppose Parliament passes a new Act in 2025, after IP completion day, which modifies rules previously governed by a retained EU law Regulation. The new Act’s provisions conflict with the retained EU law.

Answer:
Section 5(1) of EU(WA) 2018 restores full parliamentary sovereignty as regards new legislation. The 2025 Act prevails over the pre-existing retained EU law, making the latter subordinate to the new domestic statute.

Practical Limitations: Sunset Provisions and the Evolving Status of Retained EU Law

The Retained EU Law (Revocation and Reform) Act 2023 introduces a 'sunset' whereby much retained EU law will fall away unless expressly preserved. Ministers and devolved authorities are empowered by statutory instrument to restate, amend, or repeal retained EU law. This process allows for significant revision and departure from retained EU law using delegated powers ("Henry VIII powers"), further affirming the sovereignty of Parliament—and, in many instances, the executive in practice.

These developments contribute to an ongoing, continuing process: the re-examination, amendment, and sometimes repeal of EU-derived legislation as the UK shapes its legal order post-Brexit.

Interpretation of Retained EU Law: The Role of the Courts

Section 6 of the EU(WA) 2018 provides that:

UK courts are no longer able to refer questions to the CJEU after IP completion day.
UK courts and tribunals are not bound by CJEU decisions made after IP completion day, but may "have regard" to such case law if they consider it appropriate.
Pre-IP completion day CJEU case law remains binding on lower courts in relation to retained EU law, but the Supreme Court and Court of Appeal (or equivalent appellate courts in Scotland and Northern Ireland) can depart from it if "it appears right to do so," applying a similar test to that for departing from their own previous decisions.

Courts must also interpret retained EU law in line with retained general principles (such as proportionality, equal treatment, and legitimate expectation), but only so far as they have been "recognised by the CJEU before IP completion day." General principles do not of themselves create new causes of action or provide a basis to challenge retained EU law, except to the extent expressly provided for by statute.

Notably, the Charter of Fundamental Rights of the European Union is not retained, but domestic law and retained general principles may nonetheless afford similar protection in some circumstances.

Worked Example 1.4

A party is litigating over a health and safety regulation that was formerly an EU regulation but now forms part of retained EU law. The claimant cites a post-Brexit CJEU decision interpreting a similar provision.

Answer:
The UK court is not bound by the post-IP completion day CJEU decision but may "have regard" to it. However, the court must apply and follow relevant pre-IP completion day CJEU decisions unless there are good grounds to depart (if it is the Supreme Court or Court of Appeal).

State Liability and EU General Principles after Brexit

The remedy of state liability for breaches of EU law (the Francovich principle) does not extend to breaches of retained EU law post-IP completion day, except for claims already pending or for events before that date. The principle of proportionality and legal certainty survives only insofar as these are general principles recognized before IP completion day and necessary for interpretation.

Challenging Retained EU Law and Administrative Action

Retained EU law classified as primary or secondary legislation retains its pre-exit status for most legal purposes (including for compatibility with the Human Rights Act 1998):

Primary retained EU law may be subject to a declaration of incompatibility, not invalidation, if found to contravene a Convention right under the Human Rights Act 1998.
Secondary retained EU law can be declared invalid if incompatible.

Administrative action under retained EU law can be judicially reviewed according to ordinary principles of public law, and the same procedural rights and remedies generally apply as to domestic legislative and administrative acts.

Worked Example 1.5

A piece of secondary legislation, implementing retained EU law, is amended by a statutory instrument under the powers conferred by the Retained EU Law (Revocation and Reform) Act 2023. A challenge is brought on grounds that the Minister has exceeded their delegated authority.

Answer:
The challenge is considered according to domestic administrative law principles (illegality, irrationality, procedural impropriety). The court will scrutinise whether the delegated powers under the Act have been used for a permissible purpose and within the limits imposed by the parent legislation.

Constitutional Implications

The introduction and operation of retained EU law in the UK’s legal system post-Brexit illustrates the ongoing tension between legal theory and practical governance.

From a doctrinal standpoint, Parliament’s sovereignty, as reaffirmed by s 38 EU(WA) 2018 and further emphasised in s 38 of the European Union (Withdrawal Agreement) Act 2020, is not abrogated by retained or new EU law: Parliament can expressly repeal, amend, or override any provision, constitutional or otherwise.

In practice, however, the existence of a large and complex body of retained EU law, particularly in areas closely connected to the UK’s international commitments (for instance, via the Northern Ireland Protocol or the Trade and Cooperation Agreement), means that Parliament’s power is exercised with an awareness of legal, diplomatic, and political realities.

The conferral of wide delegated powers to ministers, enabling wholesale amendment or removal of retained EU law (including the use of Henry VIII clauses), raises questions about the separation of powers and the erosion of parliamentary oversight in favour of executive discretion. This shift has constitutional significance and continues the debate about the appropriate balance of legislative and executive action in the modern constitution.

Importantly, while Parliament is legally and constitutionally permitted to override retained EU law, certain "constitutional statutes" are increasingly recognised by courts as special. Although such statutes may be repealed or amended, the courts expect explicit language and democratic debate rather than inadvertent repeal or amendment by implication. This expectation does not legally restrict Parliament but fosters constitutional stability and clarity.

Key Point Checklist

This article has covered the following key knowledge points:

Parliamentary sovereignty is the core doctrine that the UK Parliament has the legal authority to create or abolish any law, and legislation prevails over all other sources.
The ECA 1972 altered the practical operation of sovereignty by enacting the supremacy of directly effective EU law over conflicting domestic law for so long as the Act remained in force.
The Supreme Court and the House of Lords established in Factortame that, pre-Brexit, courts could disapply Acts of Parliament found to conflict with directly effective EU law, based on clear statutory language.
Retained EU law was created on IP completion day to preserve legal continuity, capturing EU-derived domestic law, direct EU legislation, and directly effective rights and principles that applied in the UK before exit.
For legislation passed before IP completion day, retained EU law continues to have a limited form of supremacy; it prevails over pre-existing UK law unless Parliament amends or repeals it.
Acts of Parliament passed after IP completion day are supreme over retained EU law, reflecting the full restoration of parliamentary sovereignty in the post-Brexit order.
The courts interpret retained EU law with reference to pre-IP completion day CJEU case law and retained general principles, but higher courts may depart from it in suitable cases.
The executive has significant delegated powers to amend, repeal, or replace retained EU law through statutory instruments under the Retained EU Law (Revocation and Reform) Act 2023, raising constitutional questions about executive authority and parliamentary scrutiny.
Constitutional statutes, while not entrenched, enjoy special status; courts expect express words before their amendment or repeal, especially if significant constitutional change is envisioned.
The principles of legal certainty, the rule of law, and parliamentary accountability continue to inform judicial reasoning in relation to the modification of retained EU law and its interaction with the wider constitution.

Key Terms and Concepts

parliamentary sovereignty
retained EU law
constitutional statutes
rule of law

Retained EU law and the UK constitution - Parliamentary sove...