Retained EU law in the UK after Brexit

The 2018 European Union (Withdrawal) Act (EUWA) provided a new constitutional framework for the continuity of this 'retained EU law' in the UK from 31 December 2020, replacing the EU treaties that had until that point applied in the UK. Thousands of amendments to that retained EU law also entered into force at the same time, so that the UK statute book was still operational in an independent legal system divorced from the EU.

The 2023 Retained EU Law (Revocation and Reform) Act has modified this framework from 1 January 2024. In particular, it has removed the special features of EU law that applied to interpretation and application of this legislation, and renamed it as ‘assimilated law’.

What was retained EU law?

Retained EU law was essentially a snapshot of EU law as it applied in the UK on 31 December 2020, which was cut and pasted into our domestic legal system. Sections 2 to 4 of EUWA establish three categories of retained EU law:

• domestic law which implemented or related to former EU obligations, such as the UK's Working Time Regulations, which implemented the EU Working Time Directive;
• EU legislation which was directly applicable in the UK without implementing legislation, such as the EU's General Data Protection Regulation; and
• other rights and principles in EU law that had direct effect in the UK, like the right not to be discriminated on grounds of nationality, which is a right provided for in the Treaty on the Functioning of the EU.

Officially, this could amount to 150,000 pieces of EU legislation, though it is thought that only a few thousand of them have a practical impact in the UK. Since 2022, the UK government has published and updated a Retained EU Law Dashboard listing the status of more than 4,000 legislative instruments that it has identified.

This covers most aspects of UK law that were previously derived or influenced by EU legislation, including environmental regulation, data protection, employment law, intellectual property, financial services, food safety, medicines regulation, and competition law.

What is assimilated law?

The first two categories of retained EU law – directly applicable EU legislation and domestic law related to former EU obligations – have been renamed as assimilated law from 1 January 2024. The third category of retained EU law, relating to EU law rights and principles, has been repealed in UK law from January 2024. The special EU law features of any former EU law have been removed, so that they do not apply when a UK court or tribunal is applying assimilated law from 2024.

This means that the principle of EU law supremacy, general principles of EU law and directly effective EU rights – all developed in EU case law – do not apply. The result is that national legislation can no longer be disapplied on the grounds that it is inconsistent with EU legislation or EU law principles.

Amendments to retained EU law

Even before the end of 2020, the UK and devolved governments made more than 1,000 pieces of domestic secondary legislation, making over 100,000 amendments to retained EU law. For the most part, these were technical, to ensure that the retained EU law would be clear and operable when applied purely in a UK domestic context.

However, there were also substantive changes, and some pieces of EU legislation were revoked entirely. Since 2020, we have also seen new primary legislation creating new post-Brexit regimes replacing retained EU law in some areas, such as agriculture and subsidy control. So, it is important to check an up-to-date version of assimilated law and retained EU law taking account of any amendments, before relying on it.

Whilst most retained EU law in the UK was initially close or even identical to the EU's own 'classic' EU law at the end of 2020, the two will inevitably diverge over time as they evolve independently of one another, save in those areas where there may be some economic or other policy interest in the UK maintaining alignment with the EU.

Enforcement and litigation issues

Much of the legislation that is assimilated law was interpreted by our courts in a particular way before Brexit, because it was based in EU law. That is no longer the case from January 2024, following the removal of special EU law features from this legislation. Therefore, previous case law relating to that legislation no longer applies, to the extent that it is based on those features.

However, other EU-based case law from judgments handed down before Brexit is still binding on UK lower courts after Brexit, unless the Court of Appeal or another higher court overrules it. New case law from the EU courts after Brexit is not binding on any UK courts.

To fill in any remaining gaps in the meaning of legislation where case law does not provide the answer, UK courts need to apply traditional domestic law principles of interpretation, instead of EU law principles. This may lead to courts reaching the same conclusions as they did before Brexit on some points of interpretation, whilst on others, they find that legislation now has a different meaning and effect without its special EU law features. This is likely to mean some uncertainty in the first few years of assimilated law from January 2024; and uncertainty usually means more litigation as people seek clarity in the law.

The 2023 Act has also created new court procedures for cases raising issues of EU-based case law, notably allowing lower courts to refer points of law to the Court of Appeal for a ruling on whether to follow the previous case law. However, these new procedures are not immediately in force from January 2024, and are expected at a later date, once each court and tribunal has had the opportunity to make detailed new rules of procedure.

Other remnants of EU law in the UK

Although not falling within the definitions of retained EU law or assimilated law, many aspects of the UK-EU Brexit deals are directly enforceable in the UK legal system in the same way that EU law was previously. Section 7A of EUWA provides for the UK-EU Withdrawal Agreement, including the Northern Ireland Protocol and the Windsor Framework supplementing it, to have direct effect in the UK legal system where the agreement requires this.

Section 29 of the 2020 European Union (Future Relationship) Act similarly makes a general modification to all existing domestic law, so far as necessary to comply with the UK-EU Trade and Cooperation Agreement. The question of how many provisions of the Brexit deals can actually be enforced in the UK courts under these general provisions is a grey area. However, it does mean in principle that, if domestic laws or administrative actions breach the agreements, then businesses and individuals can seek to have them disapplied by the UK courts.