# Retained EU law and assimilated law after Brexit

> **Key takeaway:** EUWA 2018 preserved EU-derived law; 2023 Act reforms status (assimilated law), curtails supremacy effects, eases change. CJEU case law: follow current s.6 EUWA rules. Always check amendments. Fast-moving — verify before reliance.

- **Jurisdiction:** England & Wales
- **Practice area:** Public Law
- **Last reviewed:** 2026-08-04
- **Interactive page:** https://kttclegal.info/library/notes/PublicLaw/retained-eu-law-overview
- **Keywords:** retained EU law, assimilated law, European Union Withdrawal Act 2018, REUL Act 2023, Brexit, CJEU, supremacy, IP completion day

## What is this about?

After the UK left the EU, a body of EU-derived law was preserved in domestic law to avoid cliffs. The European Union (Withdrawal) Act 2018 created 'retained EU law'; later reforms (notably the Retained EU Law (Revocation and Reform) Act 2023) re-labelled and altered its status, supremacy, and interpretation — often under the banner of 'assimilated law'. This area moves quickly; always check the current statutory position.

## What is the core rule?

EUWA 2018 preserved EU-derived domestic legislation, direct EU legislation, and certain rights in domestic law from IP completion day, subject to exceptions and later amendment. Domestic courts were directed on the status of CJEU case law (s.6 framework as amended). The 2023 Act revoked the principle of supremacy of EU law for the post-reform era, renamed retained EU law as assimilated law from the end of 2023 in relevant respects, facilitated amendment, and adjusted judicial departure from retained case law. Specific domains (e.g. data protection, competition, employment equality roots) still show EU parentage but must be read through current UK statutes and regulations.

## What are the elements or test?

1. Is the provision assimilated/retained EU law, pure domestic law, or EU law still relevant via the TCA/other treaty?
2. What does EUWA 2018 (as amended) and the 2023 Act say about its status and interpretation?
3. Does pre- or post-IP completion CJEU authority bind, guide, or merely persuade?
4. Has Parliament or ministers amended the rule since Brexit?
5. Any section 6 departure mechanism engaged for higher courts?

## Which authorities matter?

- **European Union (Withdrawal) Act 2018 (as amended)** — Foundational preservation of EU-derived law and framework for CJEU case-law status.
- **Retained EU Law (Revocation and Reform) Act 2023** — Major reform: assimilation, removal of supremacy/general principles effects as specified, and amendment powers.
- **European Union (Withdrawal Agreement) Act 2020 / UK-EU Trade and Cooperation Agreement (context)** — Implementation of the Withdrawal Agreement and ongoing treaty relationship — separate from pure REUL status but relevant in practice.

## How does this apply in practice?

This is a high-level map of a fast-changing field. Never rely on pre-2023 summaries of 'supremacy of retained EU law' without checking the 2023 Act's effects on your provision. Sector guidance (e.g. equality, working time, consumer) may have specific amendment SIs. For pure EU institutional law history, see taxonomy EU Law sub-areas still without full corpus coverage.

## What are common pitfalls?

- Citing CJEU cases as if automatically binding as before exit day
- Ignoring the 2023 Act's renaming and anti-supremacy effects
- Assuming all EU-derived rights were wiped rather than assimilated/amended
- Conflating TCA obligations with retained/assimilated domestic law

## When would a practitioner use this?

Statutory interpretation problems with EU parentage, employment/equality legacy directives, and advising on whether old EU case law still carries weight.

## Quick reference

EUWA 2018 preserved EU-derived law; 2023 Act reforms status (assimilated law), curtails supremacy effects, eases change. CJEU case law: follow current s.6 EUWA rules. Always check amendments. Fast-moving — verify before reliance.

---

*Reference material from [KTTC Legal](https://kttclegal.info/), not legal advice. Work product supports instructing solicitors and barristers under their supervision. England & Wales.*