Introduction
The United Kingdom’s withdrawal from the European Union necessitated a monumental legal undertaking: the transfer of a vast and complex body of EU law into the domestic legal system to avoid a legislative vacuum. The European Union (Withdrawal) Act 2018 (EUWA 2018) was the initial solution, creating a new category of domestic law known as ‘retained EU law’ (REUL). This framework was designed primarily to ensure legal continuity and, by extension, a degree of legal certainty in the immediate post-Brexit period. However, this arrangement was always intended to be transitional. The subsequent enactment of the Retained EU Law (Revocation and Reform) Act 2023 (REUL Act 2023) marked a significant shift in approach, renaming REUL as ‘assimilated law’ and introducing new mechanisms for its amendment, revocation, and interpretation.
This essay will evaluate whether this transition from the REUL framework to the new regime of assimilated law has improved legal certainty. Legal certainty, a cornerstone of the rule of law, requires that law is accessible, predictable, and stable, allowing individuals and businesses to order their affairs with confidence in the legal consequences of their actions (Bingham, 2010). This essay will argue that the move has demonstrably failed to improve legal certainty. While the initial REUL framework under the 2018 Act was not without its own interpretive challenges, it provided a relatively stable and predictable, if temporary, foundation. By contrast, the 2023 Act, in its pursuit of rapid legislative divergence, has introduced profound and systemic new uncertainties. These arise from the accelerated revocation process it initiated, the creation of broad executive powers to modify the law with diminished scrutiny, and a deliberate destabilisation of established interpretive principles and judicial precedent, ultimately undermining the very stability the law seeks to provide.
The Baseline for Certainty: The Retained EU Law Framework (2020-2023)
To assess whether a change has constituted an improvement, one must first understand the baseline. The EUWA 2018 was enacted with legal certainty as a primary objective. Its central mechanism was to take a legislative "snapshot" of EU law as it applied to the UK on 31 December 2020 and preserve it in domestic law as REUL. This included EU regulations, directives (as implemented), decisions, and the case law of the Court of Justice of the European Union (CJEU) that interpreted them. This "copy and paste" approach, while technically complex, provided immediate and substantial certainty for legal practitioners, businesses, and citizens. The vast majority of rules governing areas from employment rights to environmental standards simply remained the same on 1 January 2021 as they had been the day before. This continuity was a powerful, if underappreciated, source of stability.
However, the REUL framework was far from a perfect model of certainty. Its key weakness lay in the inherent tension of preserving a body of law while removing it from its parent legal order. Professor Mark Elliott described REUL as a form of "Frankenstein’s law", stitched together from EU and UK parts and animated by a different legal spirit (Elliott, 2017). This created several specific points of uncertainty.
First, the interpretive hierarchy was altered. EUWA 2018 abolished the principle of the supremacy of EU law for legislation passed after exit day. For pre-existing domestic law, however, the matter was more complex. More significantly, it addressed the role of pre-exit CJEU case law. Under section 6(3) of EUWA 2018, UK courts below the Supreme Court and Court of Appeal were bound by retained EU case law. The Supreme Court and Court of Appeal, however, could depart from it, but only by applying the same test they use to depart from their own precedents, as established in the Practice Statement (Judicial Precedent) [1966] 1 WLR 1234. This test requires the court to be convinced that it is "right to do so", a high threshold that promotes judicial caution and respects the value of precedent. This approach created a slow, judicially-led, and relatively predictable pathway for divergence, prioritising stability over rapid change. The Court of Appeal’s cautious approach in TuneIn Inc v Warner Music UK Ltd [2021] EWCA Civ 441, where it declined to depart from CJEU precedent, exemplified the judiciary’s initial commitment to this stable evolution.
A second source of uncertainty arose from the status of the general principles of EU law (e.g., proportionality, legal certainty, legitimate expectations). Section 5(4) of EUWA 2018 preserved these principles for the purpose of interpreting REUL. However, section 5(5) stipulated that they could not be used to ground a new cause of action or to invalidate primary legislation. This created a nebulous role for principles that were once a powerful engine of EU law, leaving their precise effect on the interpretation of REUL unclear (Craig, 2018).
Despite these inherent tensions, the REUL framework established by EUWA 2018 provided a high degree of short-to-medium-term legal certainty. The vast corpus of law was unchanged, and the mechanism for future change was judicial, cautious, and tethered to established common law principles of stare decisis. It was against this baseline of imperfect but functional certainty that the 2023 Act was passed.
The 2023 Act: A Paradigm Shift Towards Uncertainty
The REUL Act 2023 was driven by a political desire to accelerate the process of divergence and "end the special status of EU law" in the UK statute book (UK Government, 2022). While its stated aims included providing clarity, the mechanisms it introduced have systematically prioritised legislative flexibility over legal certainty. The Act has achieved this through three primary means: the process of revocation, the expansion of executive power, and the active encouragement of judicial instability.
The Uncertainty of the Revocation Process
The Act’s most notorious feature was the original ‘sunset’ clause, which would have automatically revoked the majority of REUL at the end of 2023 unless explicitly saved. This proposal generated "extreme uncertainty" across the economy, as businesses and legal advisors were unable to predict which regulations would exist in a few months' time (House of Lords Delegated Powers and Regulatory Reform Committee, 2023, p. 5). The potential for thousands of laws to vanish overnight, with unknown and unexamined consequences, represented a direct threat to the rule of law.
While the government ultimately abandoned this automatic sunset in favour of a specific list of around 600 instruments to be revoked via Schedule 1 of the Act, the episode itself damaged legal certainty. It demonstrated a governmental willingness to countenance chaotic, sweeping legal change without proper scrutiny. Furthermore, even in its revised form, the process of identifying laws for the Schedule 1 "kill list" was opaque and rushed, raising significant concerns about whether Parliament and relevant stakeholders fully understood the ramifications of each revocation (Bingham Centre for the Rule of Law, 2023). This approach, driven by a political deadline rather than a careful policy review, is the antithesis of a process designed to enhance legal certainty.
Executive Dominance and the Erosion of Certainty
Perhaps the most constitutionally significant, and most damaging for long-term legal certainty, are the sweeping powers the 2023 Act grants to government ministers. Part 2 of the Act provides powers to revoke, replace, or "restate" assimilated law using secondary legislation, which is subject to far less parliamentary scrutiny than primary legislation.
The power to "restate" assimilated law under section 12 is particularly pernicious from a certainty perspective. A restatement is intended to make the law clearer, but the Act allows a minister, in restating the law, to make provisions they consider "appropriate" to resolve "ambiguity, doubt or anomaly" or to reflect developments in case law. This effectively grants the executive a quasi-judicial power to interpret and modify the substance of the law under the guise of tidying it up. As the House of Lords Constitution Committee (2023, p. 27) warned, "this could lead to the law being changed by stealth."
This creates a new and alarming layer of uncertainty. The law on a given topic will no longer just be what is written in the statute and interpreted by the courts; it will also be what a minister believes it should mean. A business seeking to comply with complex environmental or financial regulations can no longer rely solely on judicial precedent; it must also be wary of a future statutory instrument, passed with minimal debate, that retrospectively "clarifies" the law in a way that alters its substantive obligations. This shift from a system where legal development is primarily led by Parliament and the judiciary to one where the executive has broad powers to amend the law undermines the separation of powers and, with it, the predictability that is essential for legal certainty.
The Destabilisation of Precedent and Interpretation
The REUL Act 2023 directly attacks the foundations of legal certainty by destabilising the body of case law that explains what assimilated law means. It does this in two principal ways: by abolishing the general principles of EU law and by making it much easier for courts to overturn established precedents.
First, section 4 of the Act abolishes the interpretive effect of the general principles of EU law. These principles provided a crucial context for understanding laws that were drafted with them in mind. Their removal leaves an interpretive vacuum. How should a court now interpret a provision on, for example, equal pay or environmental protection, which was designed to be read in light of principles like effectiveness, proportionality, and non-discrimination? The Act provides no answer, creating significant ambiguity. This forces courts to choose between interpreting the text in a historical context that has been legislatively abolished or treating it as ordinary domestic legislation, which could radically alter its meaning and effect (Barnard, 2023). This is a recipe for litigation and uncertainty.
Second, and more fundamentally, section 6 of the Act replaces the cautious EUWA 2018 test for departing from retained EU case law. The high threshold of the Practice Statement test is gone. Instead, the Supreme Court and Court of Appeal must simply consider whether it is "appropriate" to depart from a precedent. Section 6(5) provides a non-exhaustive list of factors to consider, including the fact that decisions of a foreign court are not "normally binding" and that retention of the case law "would be inconsistent with any developing area of domestic law".
This change is a direct invitation to re-litigate established legal rules. It significantly lowers the bar for challenging precedent, transforming the judicial role from one of ensuring stability to one of actively seeking divergence. The Law Society (2022) rightly warned that this would "create legal uncertainty and encourage speculative litigation". A lawyer can no longer advise a client with confidence on the basis of a clear line of retained EU case law. The advice must now be heavily caveated with the possibility that a court, even a lower appellate court, might find it "appropriate" to chart a new course. This is a dramatic departure from the common law tradition of stare decisis, which values an incremental and predictable evolution of the law. The 2023 Act, by contrast, prioritises the political goal of divergence at the direct expense of doctrinal stability and legal certainty.
Conclusion
The transition from the framework of retained EU law to that of assimilated law has not improved legal certainty; on the contrary, it has actively and substantially diminished it. The initial REUL system, born from the EUWA 2018, was a pragmatic compromise designed to ensure continuity. While it contained inherent interpretive difficulties, its reliance on a high threshold for judicial departure and the preservation of the existing legal corpus provided a crucial measure of stability in the turbulent post-Brexit environment.
The REUL Act 2023 represents a decisive move away from this stability-focused model. Its original sunset clause threatened a chaotic bonfire of regulations, and while this was averted, the process has left a legacy of rushed and poorly scrutinised legislative change. More enduringly, the Act has created new and profound sources of uncertainty. It has endowed the executive with broad, ill-defined powers to alter the law via secondary legislation, blurring the lines between executive and judicial functions and reducing parliamentary oversight. It has created an interpretive vacuum by abolishing the general principles of EU law without providing a clear substitute. Most significantly, it has deliberately destabilised the system of precedent by replacing a high bar for departing from established case law with a vague and permissive test that invites speculative litigation.
In seeking to rapidly unshackle the UK from the legacy of EU law, the government has prioritised political symbolism and legislative speed over the fundamental rule of law principle of legal certainty. The result is a legal landscape that is less predictable, less stable, and more prone to challenge than it was under the initial REUL framework. The move to assimilated law has, therefore, not been an improvement for legal certainty but a significant and potentially damaging step backwards.
References
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