The Legal Consequences of Brexit: Retained EU Law, Assimilated Law, and Legal Continuity
Last updated on September 21, 2026
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This analysis is part of our comprehensive reference guide on Foundations of Law.
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The Legal Consequences of Brexit: Retained EU Law, Assimilated Law, and Legal Continuity
Introduction
Brexit did not mean that the entire body of European Union-derived law suddenly disappeared from the United Kingdom’s legal system.
That would have created enormous legal uncertainty.
For decades, EU law had influenced almost every major area of economic and public life in the United Kingdom. It affected employment, consumer protection, environmental regulation, financial services, intellectual property, transport, agriculture, product standards, data protection, competition, and many other areas.
Simply removing all of those rules on the day the United Kingdom ceased to be subject to EU law would have left thousands of legal gaps.
The UK therefore adopted a system of legal continuity.
The central mechanism was created by the European Union (Withdrawal) Act 2018. It provided for a large body of EU-derived rules to continue in domestic law after the end of the transition period. This body became known as retained EU law, commonly abbreviated as REUL.
The story did not end there.
The Retained EU Law (Revocation and Reform) Act 2023 substantially changed the framework. From 1 January 2024, much of the retained EU law that remained in force became known as assimilated law. The special EU-law interpretive features attached to retained EU law were largely removed, and the surviving rules became part of domestic law under a more distinctly UK legal framework.
By 2026, another important stage had been reached. The majority of the special powers created by the 2023 Act expired on 23 June 2026. The government can nevertheless continue to amend or repeal assimilated law through other domestic legislative powers. The final official parliamentary report was published in July 2026.
The legal consequences of Brexit therefore cannot be understood simply by asking:
“Did EU law disappear?”
A better question is:
“Which EU-derived rules survived, in what form, under what interpretive principles, and how can they now be changed?”
That question reveals the real constitutional significance of Brexit.
1. What Changed When the United Kingdom Left the European Union?
The United Kingdom formally left the European Union on 31 January 2020.
However, EU law did not cease to have domestic relevance immediately.
A transition period followed, during which most EU law continued to apply to the UK.
The transition period ended on 31 December 2020.
From that point, the United Kingdom was no longer an EU Member State, and the domestic legal relationship with EU law fundamentally changed.
Yet the government and Parliament faced a practical problem.
Thousands of domestic legal rules had been created because of EU membership.
Some were contained in UK Acts of Parliament.
Others were contained in statutory instruments made to implement EU obligations.
Still others consisted of directly applicable EU regulations and other EU-derived legal instruments.
If all of these rules simply ceased to operate, there could have been immediate uncertainty concerning rights, duties, regulatory standards, and commercial arrangements.
The solution was legal continuity.
2. The European Union (Withdrawal) Act 2018
The principal statutory foundation for the transition was the European Union (Withdrawal) Act 2018.
The Act was designed, among other things, to ensure that the UK statute book would continue to function when EU law ceased to apply automatically as a consequence of membership.
The legislation created the category known as retained EU law.
The basic idea was relatively straightforward:
EU-derived rules that were already operating within the domestic legal system would, subject to important exceptions and modifications, be preserved rather than simply disappear.
This allowed businesses, individuals, courts, regulators, and public authorities to continue operating under a substantially continuous legal framework immediately after the end of the transition period.
3. Why Was Retained EU Law Necessary?
Imagine that a legal rule regulating a particular commercial activity had applied for twenty years.
Businesses had structured their contracts around it.
Courts had interpreted it.
Regulators had incorporated it into their procedures.
Consumers had relied upon it.
If that rule suddenly vanished on 1 January 2021, the consequences could have been substantial.
There might have been:
- regulatory gaps;
- uncertainty about contractual obligations;
- conflicting interpretations;
- missing technical standards;
- uncertainty concerning existing rights;
- disruption to business operations; and
- a significant increase in litigation.
Retained EU law was therefore primarily a mechanism of legal continuity.
It did not mean that the United Kingdom remained legally subject to the European Union.
It meant that many EU-derived rules were transferred or preserved within the domestic legal system so that the UK could continue functioning with a stable body of law.
The official government explanation of the framework identifies legal continuity and certainty at the end of the transition period as the principal purpose of retained EU law.
4. What Was Retained EU Law?
Retained EU law was not one single Act or one single collection of rules.
It was a category of domestic law containing different kinds of legal material.
It included, subject to the statutory framework:
- EU-derived domestic legislation;
- certain directly applicable EU legislation;
- certain rights and obligations preserved by the Withdrawal Act; and
- case law associated with the retained body of law.
This produced an unusual legal category.
The rules had become part of UK domestic law, but they carried with them certain characteristics inherited from their EU origins.
That special status became increasingly controversial and eventually led to the reforms introduced by the 2023 Act.
5. Retained EU Law Was Domestic Law
One of the most important points is that retained EU law was domestic law.
After the end of the transition period, a retained EU regulation was not simply functioning because the UK remained an EU Member State.
The United Kingdom had left the EU.
The relevant legal rule operated because Parliament had created a domestic statutory mechanism preserving it.
This distinction is crucial.
A rule could have originated in EU law but become part of UK law through the European Union (Withdrawal) Act 2018.
Its continuing legal authority therefore depended upon UK domestic law.
This is one of the clearest examples of how Brexit transformed the constitutional status of EU-derived rules without necessarily eliminating their substantive content.
6. Retained EU Law and the Principle of Legal Continuity
The idea of continuity was broader than simply preserving individual regulations.
The UK legal system needed continuity at several levels.
There had to be continuity of:
- legislation;
- rights and obligations;
- regulatory standards;
- judicial interpretation;
- administrative systems; and
- commercial expectations.
The Withdrawal Act therefore attempted to preserve a functioning legal environment while changing the constitutional relationship between UK law and EU law.
This was an extraordinary legal exercise.
The challenge was essentially:
How can a state leave a supranational legal order without simultaneously destroying the domestic legal rules that developed under that order?
Retained EU law was one answer to that problem.
7. The Special Status of Retained EU Law
Retained EU law was not originally treated exactly like ordinary domestic legislation.
The European Union (Withdrawal) Act 2018 created special rules concerning:
- the supremacy of EU law in certain circumstances;
- general principles of EU law;
- the interpretation of retained EU law; and
- the status of retained EU case law.
These special features reflected the legal history of the rules.
Although they had become domestic law, Parliament initially preserved some of the interpretive characteristics that had applied while the UK was an EU Member State.
This created a hybrid legal category.
It was neither ordinary EU law nor entirely ordinary UK legislation.
8. The Supremacy of EU Law
One of the most important concepts associated with EU membership was the supremacy of EU law.
Within the EU legal order, EU law could take precedence over conflicting domestic law in circumstances falling within the scope of EU law.
The European Union (Withdrawal) Act 2018 preserved a limited version of this principle for certain retained EU law.
The purpose was continuity.
If a domestic rule had previously been subject to the priority of EU law, simply leaving the EU could otherwise have radically altered the legal position overnight.
The 2018 Act therefore preserved aspects of the old relationship for the purposes of the retained body of law.
The 2023 Act subsequently abolished the supremacy principle as it applied within retained EU law. The explanatory notes expressly describe this as one of the major changes introduced by the Act.
9. General Principles of EU Law
Another feature of retained EU law was the continued relevance of certain general principles of EU law.
These principles had developed through the jurisprudence of the Court of Justice of the European Union.
They could influence the interpretation and application of EU-derived rules.
The Withdrawal Act initially preserved aspects of these principles within the domestic legal system.
This was another example of the hybrid nature of retained EU law.
The United Kingdom was no longer an EU Member State, yet certain principles originating in EU law continued to have domestic legal significance because Parliament had expressly preserved them.
The 2023 reforms changed this position.
The general interpretive role of those EU principles was removed from retained EU law at the end of 2023.
10. Retained EU Case Law
The continuity problem also applied to judicial decisions.
Before Brexit, UK courts were required in appropriate circumstances to follow decisions of the Court of Justice of the European Union.
After Brexit, that relationship changed.
The European Union (Withdrawal) Act 2018 established rules governing the treatment of pre-Brexit EU case law.
Certain CJEU decisions became part of the retained legal framework.
UK courts could therefore continue to rely upon relevant EU case law when interpreting retained EU law.
But this was not intended to create a permanent obligation for UK courts to follow every future decision of the CJEU.
The distinction between pre-Brexit retained case law and post-Brexit CJEU decisions became particularly important.
11. Post-Brexit Decisions of the Court of Justice
After the transition period, UK courts were no longer generally bound by new decisions of the Court of Justice in the way they had been while the UK was an EU Member State.
However, subsequent CJEU decisions could still sometimes be relevant or persuasive.
A UK court might consider a later European judgment if it helps explain the historical meaning or development of an EU-derived concept.
But the constitutional relationship is fundamentally different.
The UK Supreme Court and other domestic courts are not simply subordinate to the CJEU.
The significance of this distinction is one of the major constitutional consequences of Brexit.
12. The Retained EU Law (Revocation and Reform) Act 2023
The next major stage came with the Retained EU Law (Revocation and Reform) Act 2023.
The Act received Royal Assent on 29 June 2023.
Its purpose was to remove the special status of retained EU law and provide mechanisms for revoking, replacing, or reforming the surviving body of law.
The official explanatory notes describe the Act as designed to enable amendment of retained EU law and remove its special features within the UK legal system.
The legislation represented a significant constitutional shift.
The question was no longer simply:
“How can EU-derived rules be preserved?”
It became:
“How should those rules function as ordinary domestic law after Brexit?”
13. From Retained EU Law to Assimilated Law
One of the most visible changes took effect on 1 January 2024.
Retained EU law that remained in force was renamed assimilated law.
This was not merely a change of vocabulary.
The new terminology reflected substantive constitutional changes.
The official explanatory notes to the 2023 Act state that retained EU law remaining in force after the end of 2023 became assimilated law and that it was no longer interpreted using the special retained-EU-law interpretive principles.
The conceptual shift can therefore be summarised as follows:
Retained EU law
→ a transitional category preserving EU-derived rules with special EU-related characteristics.
Assimilated law
→ surviving domestic law that no longer possesses that special EU-law status.
14. Why Was the Word “Assimilated” Chosen?
The word assimilated expresses an important constitutional idea.
The surviving rules were increasingly being treated as part of the ordinary domestic legal landscape.
They were no longer supposed to stand apart as a special category simply because they originated in EU law.
The objective was to integrate them into the domestic legal system.
This does not mean that their historical origin became irrelevant.
A lawyer may still need to understand an EU directive, regulation, or CJEU judgment to understand why a particular rule exists.
But its present legal status is determined primarily by UK domestic law.
15. The End of the Special Interpretive Rules
One of the most important consequences of the 2023 Act was the removal of special interpretive rules associated with retained EU law.
The Act abolished the retained EU-law principles of interpretation.
It also abolished the special status associated with the supremacy of EU law.
As a result, assimilated law is interpreted under domestic legal principles rather than under the special interpretive framework inherited from EU membership.
This is one of the clearest ways in which Brexit changed the legal architecture even where the wording of a particular rule remained substantially unchanged.
The same words can exist within a different constitutional framework.
16. What Happened to Retained EU Case Law?
The 2023 reforms also changed the treatment of retained EU case law.
The objective was to make it easier for domestic courts to move away from certain retained EU precedents where the statutory conditions for doing so are satisfied.
This did not mean that all previous European case law suddenly became irrelevant.
Earlier decisions can remain highly significant for understanding the meaning and development of assimilated law.
But their authority is now understood through a domestic legal framework.
The change therefore concerns constitutional status, not simply the historical value of the decisions.
17. What Was the “Sunset”?
One of the most discussed aspects of the 2023 legislation was the proposed sunset of retained EU law.
The original legislative approach contemplated that specified retained EU laws would cease to exist automatically unless preserved.
A substantial body of EU-derived legislation was therefore reviewed and classified.
The final legislation revoked a specified list of instruments at the end of 2023.
However, the surviving body of retained EU law did not disappear.
Instead, much of it continued as assimilated law.
This is an important distinction.
The phrase “Brexit abolished retained EU law” is therefore incomplete.
A substantial amount of EU-derived law survived, but in a different legal form.
18. How Much EU-Derived Law Survived?
The quantity of surviving EU-derived legislation has been substantial.
The UK government’s final official dashboard, updated in July 2026, records 6,921 individual pieces of retained EU law and assimilated law identified across approximately 400 policy areas as part of the government’s tracking exercise.
This figure should not be interpreted as meaning that 6,921 completely independent legal regimes remain unchanged.
Some instruments overlap.
Some have been amended.
Some have been revoked or reformed.
Some records represent individual pieces of legislation within larger regulatory frameworks.
The figure nevertheless illustrates the scale of the legal inheritance from EU membership.
19. Revocation and Reform
The 2023 Act did not merely rename retained EU law.
It created mechanisms for revoking, replacing, restating, or reforming elements of the inherited body of law.
This allowed the government and Parliament to change rules that had originated in the EU legal framework.
The official government reports show that reform continued throughout 2024, 2025, and 2026. The final reporting period ended on 23 June 2026. By that point, the government reported that 2,700 instruments had been revoked or reformed.
These reforms demonstrate an important feature of Brexit:
legal continuity did not mean permanent legal immobility.
Continuity was the starting point, not necessarily the final destination.
20. The Position in 2026
The current position is particularly important because older articles about Brexit can now be misleading.
As of 2026:
- “retained EU law” is largely a historical term for the body of law as it existed before the 2024 changes;
- surviving retained EU law became “assimilated law” from 1 January 2024;
- the special retained-EU interpretive effects were removed;
- EU supremacy was abolished within the retained-law framework;
- general principles of EU law ceased to have their former interpretive role;
- retained EU case law became assimilated case law;
- substantial numbers of instruments have been revoked or reformed; and
- most of the special powers under the 2023 Act expired on 23 June 2026.
The government can nevertheless continue changing assimilated law using other domestic legislation.
This means that the legal story has moved from transition to domestic maintenance and reform.
21. The Expiry of the Majority of REUL Act Powers
The date 23 June 2026 is particularly significant.
The final statutory reporting period under the 2023 Act ended on that date, and the majority of the Act’s special powers expired.
This marks an important transition.
The UK government is no longer operating a special, indefinite programme of reform based upon the reporting framework created by the 2023 Act.
Instead, changes to assimilated law can continue through ordinary domestic legislative mechanisms.
The official final report expressly states that the government can continue making changes to assimilated law through other domestic legislation.
Thus, Brexit-related legal reform continues, but the special transitional machinery is being wound down.
22. Legal Continuity Does Not Mean Legal Identity
A particularly important distinction is between continuity and identity.
A legal rule may survive Brexit without remaining legally identical in every respect.
For example, its wording may remain largely unchanged while:
- its interpretive principles change;
- its relationship with other legislation changes;
- its constitutional status changes;
- its relationship with EU institutions changes; or
- domestic courts acquire greater freedom to depart from earlier EU-related jurisprudence.
The law can therefore be substantively continuous while constitutionally transformed.
This is one of the most important concepts for understanding post-Brexit law.
23. The Difference Between Origin and Current Authority
A rule can have a European origin without remaining European law.
Consider a hypothetical regulation that was originally created at EU level and became part of UK domestic law through the withdrawal framework.
Its historical origin is European.
Its current legal authority may be entirely domestic.
This distinction is essential.
Legal researchers should therefore avoid assuming:
“This rule came from the EU, therefore EU law still governs it.”
That conclusion may be incorrect.
The better question is:
What is the present domestic legal status of the rule?
24. Brexit and Parliamentary Sovereignty
Brexit also has an important constitutional dimension concerning parliamentary sovereignty.
The EU legal order involved a relationship in which EU law had priority within its field of application and the Court of Justice had an authoritative role in interpreting EU law.
The post-Brexit framework reverses that constitutional relationship.
Parliament has created domestic rules determining the status of former EU-derived law.
Parliament can subsequently amend or repeal those rules.
The legal authority of the surviving body therefore rests upon domestic constitutional arrangements.
The 2023 reforms made this particularly clear by removing the special status of assimilated law.
25. Brexit and the Courts
The courts continue to play a major role in interpreting post-Brexit law.
Judges may have to determine:
- whether a particular rule is assimilated law;
- whether it has been amended;
- whether an EU-derived principle remains relevant;
- how pre-Brexit case law should be treated;
- whether a later CJEU decision is persuasive;
- how domestic legislation interacts with assimilated legislation; and
- whether a statutory provision has replaced an earlier EU-derived rule.
This means that Brexit did not reduce the importance of judicial interpretation.
In some respects, it made the task more complex because lawyers must understand both the historical EU position and the current domestic framework.
26. Brexit and the Court of Justice of the European Union
The Court of Justice remains an important historical source when researching EU-derived legislation.
However, its constitutional position in relation to UK courts has fundamentally changed.
The CJEU is no longer the final judicial authority for the UK’s domestic legal system.
UK courts may sometimes consider CJEU decisions, particularly where they help explain the historical meaning of a provision derived from EU law.
But the domestic legal authority of a CJEU decision now depends upon the applicable UK legal framework.
This is another example of the difference between historical influence and current legal authority.
27. The Withdrawal Agreement and Other Brexit-Related Rights
Not all EU-related domestic law became assimilated law.
This is an important qualification.
The European Union (Withdrawal) Act 2018 contains provisions dealing with rights and obligations arising under the Withdrawal Agreement and related separation agreements.
The Retained EU Law (Revocation and Reform) Act 2023 expressly preserved the operation of relevant separation agreement law. The explanatory notes distinguish this category from assimilated law.
Accordingly, a researcher should not assume that every post-Brexit EU-related rule belongs to the same legal category.
The precise statutory source must be identified.
28. Brexit and Devolution
The consequences of Brexit also interact with the UK’s devolution arrangements.
England and Wales, Scotland, and Northern Ireland do not all have identical constitutional arrangements.
The retained and assimilated law framework has therefore operated across different areas of competence.
The government’s official dashboard notes that its catalogue includes UK legislation within reserved and mixed/devolved competence but does not include legislation made by the devolved governments or legislatures.
This is important when studying the law applicable specifically in England and Wales.
The same historical EU-derived rule may have been treated differently across jurisdictions or may have been modified by legislation enacted under different constitutional powers.
29. Brexit and the Law of England and Wales
For the England and Wales portal, the consequences of Brexit should be understood as part of the broader evolution of the domestic legal system.
England and Wales remain one legal jurisdiction.
The courts now operate in a post-EU constitutional environment.
EU-derived rules that survived are increasingly integrated into domestic law as assimilated law.
At the same time, new Acts of Parliament and statutory instruments can modify the legal landscape.
This means that a lawyer researching an area such as employment, intellectual property, consumer protection, environmental law, or commercial regulation may encounter three historical layers:
pre-Brexit EU law
post-Brexit retained/assimilated law
new domestic legislation
Understanding the relationship between those layers is often essential.
30. Examples of Areas Affected by the Transition
The legacy of EU law can be found across many areas.
Examples include:
Employment law
Many employment protections developed or were significantly influenced by EU legislation and case law.
Consumer protection
Consumer rights have been shaped by numerous EU-derived measures, many of which became part of domestic law.
Environmental law
Environmental standards and regulatory frameworks contain substantial EU-derived elements.
Intellectual property
EU law has influenced several areas of intellectual property, although the precise post-Brexit position differs by right and legal regime.
The UK Intellectual Property Office explains that the 2023 Act changed the status and treatment of retained EU law affecting intellectual property.
Commercial and financial regulation
Businesses continue to operate under rules that may have originated in EU legislation but now form part of the domestic regulatory framework.
The significance of Brexit therefore extends far beyond constitutional theory.
It affects ordinary legal research.
31. A Continuing Process Rather Than a Single Event
Brexit is sometimes described as if it were a single legal event.
In reality, it produced a sequence of constitutional and legislative stages:
2016
The referendum.
2018
The European Union (Withdrawal) Act establishes the domestic framework for withdrawal and future legal continuity.
2020
The UK formally leaves the European Union.
31 December 2020
The transition period ends.
2021 onward
Retained EU law operates as part of domestic law.
29 June 2023
The Retained EU Law (Revocation and Reform) Act receives Royal Assent.
1 January 2024
Surviving retained EU law becomes assimilated law and the special retained-EU interpretive framework is substantially removed.
2024–2026
Assimilated law is progressively revoked and reformed.
23 June 2026
Most special powers under the 2023 Act expire and the final statutory reporting period ends.
2026 onward
Assimilated law continues to form part of domestic law unless changed through applicable domestic legislation.
This chronology demonstrates that Brexit’s legal consequences have unfolded over many years.
32. Why Older Brexit Articles Can Now Be Misleading
A legal article written in 2021 or 2022 may correctly describe retained EU law as the current framework.
But that terminology may now be outdated.
Since 1 January 2024, surviving retained EU law has generally been referred to as assimilated law.
Similarly, an older article may state that EU general principles continue to govern interpretation or that EU supremacy continues to apply.
Those statements cannot simply be carried forward without qualification.
The legal framework has changed.
This is why Brexit-related legal content requires particularly careful updating.
33. How to Research Assimilated Law Today
A practical research process should begin with the current domestic legislation.
A researcher should ask:
- What is the current version of the rule?
- Is it primary or secondary legislation?
- Is it assimilated law?
- Has it been amended since 2024?
- Has it been revoked?
- Has another statutory instrument replaced or modified it?
- Is there relevant domestic case law?
- Is there relevant pre-Brexit EU case law?
- Does a later CJEU decision have persuasive relevance?
- Does the Withdrawal Agreement create a separate legal issue?
The official government Retained EU Law and Assimilated Law Dashboard provides a useful starting point for identifying the status and history of many instruments. The final dashboard was updated in July 2026.
However, the dashboard should not replace checking the current text of the legislation itself.
34. The Importance of Checking the Current Statute Book
Legal continuity does not mean that a rule has remained unchanged.
An assimilated regulation may have been:
- amended;
- revoked;
- replaced;
- restated;
- transferred into another instrument; or
- affected by subsequent primary legislation.
The existence of an entry in an historical database therefore does not by itself establish the current law.
The official legislation database at legislation.gov.uk should be checked for the current statutory text.
This is especially important because the reform programme has continued beyond the original Brexit transition.
35. The Meaning of “Legal Continuity”
Legal continuity is ultimately about preventing a constitutional transition from producing unnecessary legal chaos.
The UK could leave the European Union while maintaining a functioning domestic legal system.
Businesses could continue to rely on familiar regulatory structures.
Courts could continue applying established legal rules.
Individuals could continue to understand many of their existing rights and obligations.
The system could then be changed gradually through Parliament and other domestic law-making mechanisms.
This is why the retained-law framework was so important.
It created a bridge between two constitutional eras.
36. The Meaning of “Legal Divergence”
Continuity is only one side of the story.
The other is divergence.
Once EU law ceased to have automatic domestic supremacy and the special retained-law framework was dismantled, the UK gained greater freedom to modify rules that had previously been shaped by EU law.
Over time, UK law can therefore diverge from EU law.
This does not necessarily happen immediately.
A rule can remain substantially identical for years after Brexit.
Divergence occurs when one legal system changes while the other does not, or when both systems change in different directions.
The practical significance of divergence can be substantial for businesses operating across the UK and EU.
37. The Difference Between Brexit and Automatic Deregulation
Another important misconception is that Brexit automatically removed EU-derived regulation.
It did not.
The legal continuity framework preserved a large body of rules.
Subsequent legislation has altered some of them.
But Brexit itself was not equivalent to an immediate abolition of regulatory law.
Instead, it changed who had ultimate legal authority to determine the domestic rules and how those rules could subsequently be changed.
That constitutional distinction is more accurate than describing Brexit simply as either deregulation or continued EU regulation.
38. A Constitutional Transformation
The deeper significance of Brexit lies in constitutional structure.
Before Brexit, EU law formed part of a supranational legal order in which the UK participated.
After Brexit, EU-derived rules that survived did so because of domestic legislation.
The United Kingdom therefore moved from:
membership within a supranational legal order
to:
domestic control over a body of law that had been heavily influenced by that order.
The transition was not instantaneous.
The retained-law framework made it possible for the substantive rules to survive while their constitutional foundation changed.
The later transformation into assimilated law completed another stage of that process.
39. Philosophical Insight: Can Law Leave Without Disappearing?
Brexit presents an interesting philosophical question about the nature of law.
Suppose a rule originates in one legal system.
It is then transferred into another legal system.
Does it remain the same law?
The answer depends on what we mean by “same.”
Its words may remain unchanged.
Its practical effect may initially remain unchanged.
Its historical origin remains unchanged.
But its source of authority can change.
Its interpretive framework can change.
The institutions responsible for its development can change.
Its relationship with other legal rules can change.
Brexit therefore demonstrates that the identity of a legal rule is not determined solely by its wording.
The legal system in which a rule exists is part of the meaning of the rule itself.
40. Facts: Brexit and the Post-EU Legal Framework
The essential facts are these:
- The UK left the European Union on 31 January 2020.
- The transition period ended on 31 December 2020.
- The European Union (Withdrawal) Act 2018 created the framework for retaining large amounts of EU-derived law.
- Retained EU law became domestic law rather than continuing to apply because of UK EU membership.
- The Retained EU Law (Revocation and Reform) Act 2023 substantially changed the framework.
- From 1 January 2024, surviving retained EU law became known as assimilated law.
- The special interpretive effects associated with EU law were removed from this body of domestic law.
- The supremacy of EU law was abolished within the retained-law framework.
- General principles of EU law ceased to have their previous interpretive role.
- The treatment of retained EU case law was changed.
- A significant number of EU-derived instruments have since been revoked or reformed.
- The government’s final 2026 dashboard identified 6,921 pieces of retained EU law and assimilated law in its catalogue.
- By the end of the final reporting period on 23 June 2026, the government reported that 2,700 instruments had been revoked or reformed.
- Most of the special powers created by the 2023 Act expired on 23 June 2026.
- Assimilated law nevertheless remains part of domestic law unless and until changed through applicable legislation.
41. Key Takeaways
Brexit did not simply erase EU-derived law from the UK statute book.
The United Kingdom initially preserved much of that law through the retained EU law framework.
The purpose was legal continuity.
The Retained EU Law (Revocation and Reform) Act 2023 then changed the framework fundamentally.
From 1 January 2024, surviving retained EU law became assimilated law.
The special features inherited from EU membership—including the relevant form of EU supremacy and general interpretive principles—were removed.
The surviving rules consequently became more fully integrated into domestic law.
The reform process continued through 2026, and the majority of the special powers under the 2023 Act expired on 23 June 2026.
Yet the process of changing assimilated law has not ended.
The important distinction is therefore:
Brexit created legal separation from the EU, while retained EU law created legal continuity within the UK. The later assimilated-law framework transformed that inherited body of rules into a more ordinary category of domestic law.
Frequently Asked Questions
What is retained EU law?
Retained EU law was a category of UK domestic law created principally through the European Union (Withdrawal) Act 2018 to preserve many EU-derived rules after the end of the Brexit transition period.
Does retained EU law still exist?
The term “retained EU law” is now largely historical. Surviving retained EU law became known as assimilated law from 1 January 2024.
What is assimilated law?
Assimilated law is domestic law that was previously retained EU law and remained in force after the end of 2023. It no longer has the special EU-law interpretive status that applied to retained EU law.
Does EU law still apply in the UK?
EU law no longer applies domestically simply because the UK is an EU Member State; the UK is no longer a Member State. However, EU-derived rules remain present in UK domestic law, including assimilated law, and certain provisions connected with the Withdrawal Agreement continue to have legal effect.
Can UK courts still consider decisions of the Court of Justice of the European Union?
Yes. The legal significance of a CJEU decision depends on when it was made, the nature of the relevant domestic legislation, and the applicable rules concerning precedent and persuasive authority. Post-Brexit CJEU decisions do not have the same binding constitutional status they had when the UK was an EU Member State.
Did Brexit immediately remove EU regulations from UK law?
No. The withdrawal legislation was specifically designed to preserve legal continuity. Many EU-derived rules continued in domestic law and were subsequently classified as retained EU law and then assimilated law.
What happened to the supremacy of EU law?
The Retained EU Law (Revocation and Reform) Act 2023 abolished the retained-law form of EU supremacy. The government explanatory notes identify abolition of supremacy as one of the principal reforms introduced by the Act.
What happened to general principles of EU law?
The 2023 Act removed the general principles of EU law from their former interpretive role within retained EU law. Assimilated law is therefore interpreted under domestic principles rather than the special retained-EU framework.
Can assimilated law be changed?
Yes. Assimilated law can be amended, revoked, replaced, or reformed through applicable domestic legislation. The special powers created by the 2023 Act were subject to statutory limits, and most of those powers expired on 23 June 2026.
Has all assimilated law now been reviewed?
The UK government’s final statutory reporting and dashboard exercise concluded in 2026. The final dashboard recorded 6,921 pieces of retained EU law and assimilated law and reported that 2,700 instruments had been revoked or reformed by the end of the final reporting period.
Does assimilated law apply in England and Wales?
Where an assimilated legal rule forms part of the applicable law of England and Wales, it continues to operate unless it has been amended, revoked, replaced, or otherwise affected by later legislation.
Is assimilated law the same as EU law?
No. Assimilated law is domestic UK law. It may have originated in EU law, but its present legal authority comes from the UK domestic legal framework.
Why is legal continuity important?
Without legal continuity, the UK’s departure from the EU could have created large gaps and uncertainty across areas of law that had developed under EU membership. The retained-law framework allowed the legal system to continue functioning while Parliament and government gradually reviewed and changed the inherited rules.
Conclusion
Brexit changed the constitutional relationship between the United Kingdom and the European Union, but it did not erase decades of EU influence from the British legal system overnight.
The European Union (Withdrawal) Act 2018 provided the mechanism for preserving much of the existing legal framework.
The result was retained EU law.
The Retained EU Law (Revocation and Reform) Act 2023 then began a second phase.
From 1 January 2024, surviving retained EU law became assimilated law, while the special EU-law principles that had accompanied retained EU law were substantially removed.
By June 2026, the special reform machinery established by the 2023 Act had reached another constitutional milestone, with most of its powers expiring. Yet assimilated law remains part of the domestic legal landscape and can continue to be changed through other domestic legislative mechanisms.
The history of Brexit law is therefore not a story of simple disappearance.
It is a story of transition, preservation, transformation, and eventual divergence.
The legal system first needed to preserve the rules inherited from EU membership. It then began transforming those rules into ordinary domestic law.
For lawyers, students, businesses, and members of the public, the practical lesson is straightforward:
When researching a rule that originated in EU law, do not ask only where the rule came from. Ask what its legal status is today.
That distinction—from European origin to domestic authority—is at the heart of understanding the post-Brexit law of England and Wales.
The information provided in this article ("The Legal Consequences of Brexit: Retained EU Law, Assimilated Law, and Legal Continuity") is for general educational and informational purposes only and does not constitute formal legal advice. Reading this content does not create an attorney-client relationship. Laws vary by jurisdiction; consult a licensed attorney for specific legal matters.
Tsvety, LL.M., M.A.
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