Retained EU law and the UK constitution - Relationship between UK law and retained EU law post-Brexit

Learning Outcomes

This article examines the relationship between UK law and retained EU law post-Brexit, including:

• the main categories of retained EU law, their statutory sources in the European Union (Withdrawal) Act 2018, and how their status as primary or secondary legislation affects amendment and repeal
• the historical operation of supremacy, direct effect, and indirect effect in the retained-EU framework, and how later statutory reform changes the current position
• the role of UK courts in interpreting and applying retained EU law, the extent to which pre-Brexit CJEU case law and general principles remain binding, and when higher courts may depart from them
• the constitutional implications of retaining, modifying, or revoking EU-derived rules for parliamentary sovereignty, democratic accountability, the rule of law, separation of powers, and the autonomy of devolved legislatures
• the impact of the Withdrawal Agreement, Northern Ireland arrangements, and devolution settlements on the domestic hierarchy of norms and on the protection of individual rights after Brexit
• practical techniques for identifying whether a provision is retained EU law, checking for subsequent amendment, and advising clients on compliance and litigation risk in fast-changing regulatory areas
• application of these principles to typical SQE1-style multiple-choice and scenario-based questions, enabling accurate issue-spotting, statutory interpretation, and constitutional analysis under exam conditions

SQE1 Syllabus

For SQE1, you are required to understand the relationship between UK law and retained EU law post-Brexit, with a focus on the following syllabus points:

• definition and categories of retained EU law
• the constitutional relationship between retained EU law and UK law, with an emphasis on parliamentary sovereignty and the rule of law
• the operation of supremacy of retained EU law as against UK enactments, and the effect on pre- and post-Brexit UK legislation
• methods of interpreting and applying retained EU law, including reference to pre-Brexit CJEU jurisprudence and the ability of UK courts to depart from such jurisprudence
• amendment, repeal, and revocation of retained EU law by Parliament and government ministers
• implications for legal practice, including identification and understanding of retained EU law, its amendment, and its enforceability before UK courts

Test Your Knowledge

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

1. What is retained EU law and which main categories does it include?
2. How does the principle of supremacy apply to retained EU law after Brexit?
3. Can Parliament amend or repeal retained EU law? If so, how does this affect parliamentary sovereignty?
4. How are UK courts required to interpret retained EU law, and can they depart from pre-Brexit CJEU case law?

Introduction

The UK's exit from the European Union was one of the most significant constitutional events in modern British history. To prevent legal vacuums and uncertainty, the European Union (Withdrawal) Act 2018 (as amended) created the historical category of retained EU law, importing large tranches of EU law into the UK legal system at the end of the transition period. As a result, understanding the relationship between that framework, later statutory reform, and core UK constitutional principles remains critical.

Post-Brexit milestones affecting retained EU law are traced from the 2016 referendum to the May 2023 Retained EU Law Reform Bill.

The interaction of retained EU law with the core structure of UK constitutional arrangements—Parliament, the courts, devolved governments, and the executive—raises issues concerning legal hierarchy, democratic legitimacy, interpretation, and the future role of the courts. This article analyses the constitutional status of that framework, how it is interpreted and applied, how later reform has changed its present-day operation, and the powers of Parliament and ministers to modify, revoke, or repeal EU-derived rules.

Key Term: retained EU law
The body of law that was EU in origin, preserved or converted into UK law by the European Union (Withdrawal) Act 2018 as it was in force in the UK at the end of the Brexit transition period (IP completion day).

When applying this framework, distinguish retained EU case law from retained domestic case law: the former binds domestic courts except the Supreme Court and Court of Appeal, which may depart where it appears right to do so. In a problem question, first identify whether the relevant authority is a CJEU decision and then ask whether the court hearing the case has power to depart from it. This makes the legal test, triggering fact, and consequence easier to separate.

Test Tip: In SQE-style questions on Relationship between UK law and retained EU law post-Brexit, identify the legal test, the triggering fact, and the consequence before choosing between similar answer options.

Current position

For current law, much surviving retained EU law became assimilated law from 1 January 2024. That means the older retained-EU model is still essential historical background, but it is no longer always the right present-tense label or hierarchy rule for surviving legislation. Separate statutory rights preserved under section 7A EUWA, especially those linked to the Withdrawal Agreement, must also be analysed separately rather than folded into the general retained-EU story.

Key Term: assimilated law
The live label, from 1 January 2024, for much surviving retained EU law. It generally operates as ordinary domestic law unless a later statute says otherwise.

Categories and Nature of Retained EU Law

Retained EU law is a composite legal category designed to ensure continued legal certainty and stability during and after Brexit. It includes several distinct sources with different constitutional origins and effects:

• EU-derived domestic legislation: UK primary and secondary legislation originally enacted to implement EU obligations, such as regulations made under the European Communities Act 1972 s.2(2) to give effect to EU Directives.
• Direct EU legislation: EU regulations, decisions, and tertiary instruments that were directly applicable in the UK prior to exit, now converted into UK law.
• Directly effective rights: Rights, powers, liabilities, obligations, and restrictions from EU Treaties or Directives that were recognised by courts before exit as having direct effect.
• Retained case law: Decisions of the CJEU (Court of Justice of the European Union) up to Brexit formed part of the historical retained-EU interpretive framework.
• General principles of EU law: Legal maxims like proportionality, legal certainty, and equality that were part of the historical retained-EU framework, but no longer provide the general default framework for assimilated law.

Key Term: EU-derived domestic legislation
Domestic UK statutes (primary legislation) or statutory instruments (secondary legislation) made to give effect to EU obligations—for example, regulations implementing EU Directives—retained as UK law.

The two categories also differ in how they entered the domestic constitutional framework. EU-derived domestic legislation kept its original status, so a statutory instrument made under section 2(2) of the European Communities Act 1972 remained secondary legislation rather than becoming primary law. The second category is therefore important where EU rules applied in the UK without any such implementing measure.

Key Term: direct EU legislation
EU Regulations, Decisions, and tertiary instruments that were directly applicable in the UK, now converted by the Withdrawal Act into domestic law as retained direct EU legislation.

The same preservation exercise also covered rights and obligations arising under section 2(1) of the European Communities Act 1972, where no domestic implementing measure was required. Article 157 TFEU, concerning equal pay for male and female workers, is a standard example. In an exam, distinguish this situation from direct EU legislation by asking whether the claimant relies on an individual right or on the text of an EU regulation or decision.

Key Term: directly effective rights
Rights arising from EU Treaties or Directives that—because of their clarity, precision, and unconditional character—were recognised pre-Brexit as enforceable by individuals in national courts without the need for further domestic legislation.

The retention attaches to the enforceable right rather than reproducing the Treaty article itself. Rights derived from an unimplemented Directive could generally be enforced only vertically, against the state or a state body, and only where that type of right had been recognised before IP completion day. This limited preservation should be distinguished from the separate role played by general principles of EU law in interpreting and reviewing retained rules.

Key Term: general principles of EU law
Fundamental principles, such as proportionality, legal certainty, non-discrimination, and subsidiarity, which guided the operation, interpretation, and enforcement of EU law, now retained only insofar as they were recognised before exit day.

The precise boundaries of these categories are fixed by the Withdrawal Act 2018, s.2 (EU-derived domestic legislation), s.3 (direct EU legislation), s.4 (directly effective rights), and s.6 (retained case law and general principles).

Retained EU law does not cover every aspect of EU law as it stood before exit. For example, the EU Charter of Fundamental Rights is not retained, except where its rights are found elsewhere; nor are all new post-Brexit CJEU decisions binding, although they may be considered as persuasive.

Retained EU law can also be distinguished by status:

• It can be treated as primary legislation, secondary legislation, or a novel domestic category (especially for direct EU legislation converted by s.3 and directly effective rights under s.4).
• Whether retained EU law can be amended or repealed, and what legislative procedure is required, depends on its categorisation, with some elements requiring primary legislation for amendment.

Constitutional Relationship: Supremacy and Parliamentary Sovereignty

Supremacy of Retained EU Law

Before Brexit, the supremacy of EU law meant that any conflict between EU law and UK domestic law (whenever enacted) was resolved in favour of EU law—UK courts would disapply domestic legislation, if needed, to the extent of the inconsistency (Costa v ENEL; Factortame). This supremacy was enabled (but also limited by) the European Communities Act 1972, s.2(4).

Post-Brexit, the supremacy principle initially survived in a limited form. According to the earlier Withdrawal Act framework:

• Where there is a conflict between retained EU law and UK domestic legislation enacted before the end of the transition period (i.e., pre-IP completion day), retained EU law prevails.
• However, UK legislation enacted after IP completion day (31 December 2020) takes precedence over retained EU law, unless Parliament provides otherwise.

Thus, supremacy initially operated only as a "saving" mechanism for pre-Brexit UK legislation. That historical position is constitutionally distinct from the earlier EU-membership model because Parliament remained free to legislate contrary to retained EU law after the transition period. From 1 January 2024, however, much surviving retained EU law moved into assimilated law, so that earlier limited-supremacy model is no longer the general current framework for surviving legislation.

Key Term: supremacy of retained EU law
The historical principle that, while the retained-EU framework remained in that form, some EU-derived rules could take precedence over inconsistent UK domestic legislation enacted before IP completion day. It is not the default present-tense status of assimilated law.

This approach reflects the restoration of the classical UK model of parliamentary sovereignty, limited only in respect of pre-transition UK enactments. Parliament's freedom to legislate for the future is undiminished, and so retained EU law, while privileged over certain existing statutes, is subordinate to any future legislative will.

Parliamentary Sovereignty and Amendment

Parliamentary sovereignty is a foundational doctrine of the UK constitution, supporting the notion that Parliament can make or unmake any law and cannot bind its successors. The approach to retained EU law confirms this principle:

• Parliament can amend or repeal any part of retained EU law by passing new legislation.
• Ministers are empowered (for a limited time) to correct "deficiencies" or make specific amendments to retained EU law by secondary legislation, but only under powers explicitly conferred by Parliament.

Crucially, even where the supremacy of retained EU law results in the disapplication of a pre-Brexit UK statute, Parliament can always expressly reverse this result.

Key Term: parliamentary sovereignty
The doctrine that the UK Parliament has the supreme legal authority to make or repeal any law, and that no other body can override or set aside its legislation.

The practical compromise was not that judges could strike down Acts of Parliament: under the Human Rights Act 1998, they may issue a declaration of incompatibility, but the legislation remains valid. Instead, where the wording permits, courts can seek an EU-consistent reading of domestic legislation, providing the route to the interpretative approach described next.

Key Term: indirect effect
The interpretative obligation for UK courts to construe domestic legislation, so far as possible, in line with relevant EU law and its objectives, especially where a directly effective right does not exist.

Devolution complicates the picture. The devolved legislatures in Scotland, Wales, and Northern Ireland previously could not legislate contrary to EU law within areas of devolved competence. Now, they may legislate contrary to retained EU law unless explicit restrictions remain, and retained EU law within devolved competence can be amended or repealed by the devolved legislature (subject to retained restrictions imposed by Parliament).

Worked Example 1.1

A UK statute enacted in 2013 (pre-IP completion day) is inconsistent with a retained EU regulation dealing with environmental standards. Which law takes precedence?

Answer:
The retained EU regulation prevails over the 2013 Act, as the supremacy of retained EU law operates over pre-Brexit legislation. However, Parliament could enact a post-Brexit (post-IP completion day) Act expressly or impliedly disapplying the retained EU standard, in which case the new Act would take precedence.

Interpretation and Judicial Role

Interpretation of Retained EU Law

The Withdrawal Act 2018 provides that UK courts must interpret retained EU law in accordance with pre-Brexit CJEU case law and retained general principles of EU law, unless Parliament has provided for deviation or the law has been amended. UK courts below the Court of Appeal (and equivalent) remain bound by pre-Brexit CJEU case law.

However, the Supreme Court and Court of Appeal (and equivalent higher courts) are empowered, by regulations made under s.6, to depart from retained CJEU case law "when it appears right to do so," applying the same test as they would for departing from their own previous decisions. The intention is to maintain legal certainty while allowing for organic development where justified.

Lower courts must continue to follow “retained” CJEU jurisprudence unless and until it is departed from by a higher court.

Key Term: retained EU case law
CJEU decisions handed down before IP completion day, which remain binding on UK courts when interpreting retained EU law unless and until departed from by the Supreme Court, Court of Appeal, or equivalent.

Post-transition, courts may also consider post-Brexit CJEU decisions as persuasive authority, but are not bound by them.

Indirect Effect

Historically, UK courts used indirect-effect reasoning when interpreting retained EU law and domestic measures implementing EU obligations. For current law, the court must first ask whether that earlier retained-EU interpretive framework still applies to the rule in question or whether later statutory reform has changed the position.

Where a piece of retained EU law is ambiguous, courts favour an interpretation compatible with the objective and meaning of the original EU instrument, unless post-Brexit amendments indicate a different purposive approach by Parliament.

Key Term: indirect effect
The requirement that domestic law is interpreted, so far as possible, in conformity with the objectives and wording of EU law, even where there is no directly effective right.

In practice, pre-transition CJEU decisions remain relevant when a court determines the meaning or effect of retained EU law, whereas later CJEU decisions are generally persuasive only. This distinction is subject to the separate legal arrangements preserved by the Withdrawal Agreement, which must therefore be considered before applying the ordinary post-Brexit approach.

Key Term: Withdrawal Agreement
The international treaty between the UK and EU that set out the terms of withdrawal, including the preservation of certain rights and legal arrangements during, and sometimes after, the transition period.

These rules on interpretation ensure as much legal continuity as possible, but also recognise the restored autonomy of Parliament and the flexibility for future divergence.

Worked Example 1.2

An employee brings a discrimination claim under the Equality Act 2010, arguing that a retained EU directive provides broader protection than the UK statute. How should the UK court approach this case?

Answer:
The court will interpret the Equality Act 2010, as far as possible, in line with the relevant retained EU directive and CJEU case law as it existed before IP completion day. If the UK statute is ambiguous, the court must prefer the EU-compliant interpretation. However, if Parliament amends the Equality Act 2010 post-Brexit to diverge from the directive, and the amendment is clear, the court will give effect to Parliament’s new intention.

Amendment, Revocation, and Future Developments

Amending or Repealing Retained EU Law

The Withdrawal Act 2018 gives Parliament clear authority to amend or repeal retained EU law by primary legislation. In some cases, ministers (and devolved authorities within their competence) may use specific statutory powers to address "deficiencies" or make specific amendments to retained EU law through secondary legislation, but only within statutory limits and for a defined period (initially two years post-Brexit). These powers are known as "Henry VIII clauses" and allow limited executive adjustment for technical and consequential matters arising from Brexit.

The constitutional principle remains that major policy changes, or significant shaping of UK legal standards, require primary legislation rather than mere executive action. The more important the area—such as rights, environmental protection, or consumer standards—the more Parliament is expected to legislate directly.

As retained EU law is subject to domestic modification, it becomes ever more differentiated by jurisdiction (Westminster, Scotland, Wales, Northern Ireland) and by subject matter.

Sunsetting and Further Reforms

The Retained EU Law (Revocation and Reform) Act 2023 has already changed the position substantially. It facilitated restatement, revocation, and replacement of large parts of retained EU law and, from 1 January 2024, moved much surviving REUL into assimilated law. The effect is to reduce the privileged constitutional position historically associated with retained EU law and to make ordinary domestic hierarchy rules the main starting point unless Parliament has expressly preserved a different priority.

Worked Example 1.3

A government minister seeks to use secondary legislation to make substantive policy changes to product safety standards within retained EU law. Is this permitted?

Answer:
Unless Parliament has provided explicit statutory authority for substantive policy changes (e.g., through a Henry VIII clause), a minister cannot use secondary legislation to alter the substance of retained EU law in a significant way. The limited powers to amend retained EU law by statutory instrument are intended for technical corrections and necessary changes, not policy re-writing. Major policy changes require an Act of Parliament.

Devolution, the Withdrawal Agreement, and Citizens' Rights

Brexit also impacts the distribution of legal authority within the UK. During EU membership, the devolved legislatures were required to act compatibly with EU law within areas of devolved competence (such as health or education). Following Brexit:

• UK Parliament has reserved the right to legislate for the whole UK, including in devolved areas, with or without the consent of the devolved legislatures, although the Sewel Convention provides a political (not legal) constraint that Westminster will not "normally" legislate on devolved matters without consent.
• Devolved legislatures may now amend or repeal retained EU law within areas of devolved competence unless legally constrained, leading to potential divergence of law across the UK.

The Withdrawal Agreement is significant in that it is incorporated directly into UK law by the European Union (Withdrawal Agreement) Act 2020. Some of its provisions, especially relating to citizens' rights and the Northern Ireland Protocol, have direct effect and require UK courts to give preference to Withdrawal Agreement rights over inconsistent UK legislation (mirroring the prior concept of supremacy). This ensures that certain protections endure for EU and UK citizens as agreed during the Brexit process.

Key Term: Sewel Convention
A political (not legal) convention that the UK Parliament will "not normally" legislate on devolved matters without the consent of the relevant devolved legislature.

The Sewel Convention concerns political restraint in devolved law-making, whereas the post-Brexit status of EU-derived rules is determined by legislation and applied by the courts. In an exam, distinguish conflicts with UK legislation made before the end of the transition period, where retained EU law may prevail, from conflicts with later legislation, which is not automatically subordinate. That distinction helps identify when a preserved right can be invoked in court through direct effect.

Key Term: direct effect
The principle whereby provisions of EU law, if clear, precise, and unconditional, could historically be invoked directly by individuals in national courts. After Brexit, it remains relevant chiefly where Parliament has separately preserved rights by statute, especially through the Withdrawal Agreement framework.

Practical Implications for Legal Practice

Legal professionals must be alert to the shifting boundaries and content of retained EU law. When dealing with current UK law:

• Identify whether the legislation or legal right in question is retained EU law, and if so, whether any changes have been made post-Brexit by Parliament, devolved administration, or statutory instrument.
• Advise clients on the status of retained EU law, the prospect of amendment or repeal, and the evolving relationship between retained EU law and ordinary domestic law.
• Understand the current powers of government ministers to amend retained EU law, assessing whether changes proposed or already made are within the scope of delegated authority or require primary legislation.
• When interpreting UK law, assess whether pre-Brexit CJEU decisions are binding or only persuasive in the relevant case, taking account of higher court authority.
• Monitor wider constitutional and political developments, including further Brexit-related reforms, litigation concerning retained EU law, and devolution-related legal disputes.

Revision Tip: When advising on legislative or regulatory compliance, verify whether relevant standards, rights, or duties are based wholly or partly on retained EU law and whether amendments, revocations, or regulatory reform statutes have been passed that affect their interpretation or enforceability.

Key Point Checklist

This article has covered the following key knowledge points:

• Retained EU law was the historical Withdrawal Act category used to preserve EU-derived rules after Brexit in order to maintain legal continuity.
• The retained-EU framework historically covered EU-derived domestic legislation, direct EU legislation, directly effective rights, retained EU case law, and interpretive general principles.
• The older retained-EU framework preserved a limited form of supremacy over certain pre-Brexit UK legislation, but that is no longer the general current framework for assimilated law.
• UK courts still use the historical retained-EU framework where it remains relevant, but current analysis must also account for the move to assimilated law and for any later statutory modification.
• The Withdrawal Agreement has direct effect in UK law and can override inconsistent domestic law where required by the agreement.
• The ongoing constitutional relationship between UK law and retained EU law is subject to continuous legislative and judicial development, with the scope of retained EU law liable to be reduced or transformed by further statutory reform.

Key Terms and Concepts

• retained EU law
• EU-derived domestic legislation
• direct EU legislation
• directly effective rights
• retained EU case law
• general principles of EU law
• supremacy of retained EU law
• parliamentary sovereignty
• indirect effect
• direct effect
• Withdrawal Agreement
• Sewel Convention