Assimilated case law – a paper tiger or Schrödinger’s cat?

In this post, Fabian Barth (solicitor) explores the role and impact of assimilated case law.

According to the Cambridge Dictionary, a paper tiger is something “that seems very strong and dangerous but is really weak”. Whilst there is nothing inherently dangerous about assimilated case law, it is thought to be one of the last bastions where EU law still strongly influences domestic UK law following the Retained EU Law (Revocation and Reform) Act 2023 (REULA). However, the Supreme Court might in fact see it as rather a weak concept, at least if the recent case of C G Fry & Son Ltd v Secretary of State for Levelling Up, Housing and Communities [2025] UKSC 35 (“Fry”) is to be an indicator of its views.

Background

The way by which EU law is given practical effect before the domestic courts in EU member states ordinarily follows a comprehensive system: (i) domestic law must, whenever possible, be interpreted in conformity with EU law’s substance and its general principles, (ii) failing that, EU law may (subject to further conditions) have direct effect, with the consequence that conflicting national provisions must be disapplied and (iii) the CJEU is the supreme authoritative interpreter of EU law. Following Brexit, the European Union Withdrawal Act 2018 (EUWA), broadly took a snapshot of EU law on 31^st December  2020, and retained all three limbs of its practical effect: (i) conforming interpretation still had to be applied (Section 5(2) of EUWA), as had general principles (Section 6(3)(a) of EUWA); (ii) direct effect could still be invoked (Section 4(1) of EUWA); and finally, (iii), pre-Brexit case law from the CJEU still authoritatively determined the meaning of retained EU law, unless departed from (Section 6(3)(a) of EUWA).

Within this framework, the application of CJEU case law raised no particular conceptual difficulties. Where the underlying domestic law came within the ambit of the retained supremacy of EU law under Section 5(2) of EUWA, it was clear that the courts and tribunals were obliged to decide the matter “in accordance with any retained case law”, under Section 6(3) of EUWA. Hence, whatever pertinent things the CJEU had said about the issue remained binding precedent.

For example, in Bicknell & Anor v NHS Nottingham And Nottinghamshire Integrated Commissioning Board [2026] EWCA Civ 21 (“Bicknell”), the Court of Appeal had to consider a dispute in the context of the Transfer of Undertakings (Protection of Employment) Regulations 2006 (“the TUPE Regulations”), which implemented Council Directive 2001/23/EC. The Court of Appeal held at [76] and [101] that, in the application of the regulations, it was bound by the CJEU judgment FENIN (C-205/03) [2006].

Developments following REULA

REULA, famously, significantly trimmed EUWA. For anything occurring on or after 1^st January , 2024, Section 4 of EUWA, and directly effective rights along with it, are no more. The principle of supremacy is also gone, as Section 5(A1) of EUWA now makes clear, “in relation to any enactment or rule of law (whenever passed or made)”. However, what REULA, on the face of it, did not touch is retained CJEU case law. Its label changed and it must now be called “assimilated case law” – but otherwise, Section 6(3)(a) of EUWA provides equally pre- and post-REULA that any question concerning the meaning of EU-inherited domestic law “is to be decided […] in accordance with any assimilated case law”. REULA thus engages in an interesting experiment: what is normally a harmonious and undividable framework of tools to give effect to EU law (confirming interpretation, direct effect/disapplication, case law) is attempted to be split right in the middle.

How, then, has REULA affected the effect of CJEU case law?

The obvious impression might be that REULA has not diminished the effect of CJEU case law in any relevant way. After all, where the legislation is untouched, one would normally expect its meaning and effect to stay the same, too. This insofar is the case for Section 6(3)(a) of EUWA. Practically speaking, if Bicknell had concerned events after the beginning of 2024 rather than before, one might thus reasonably think that the same outcome ought to have been reached. For events pre‑2024, the Court of Appeal considered itself bound by the CJEU case FENIN, pursuant to EUWA. Since 2024, FENIN is assimilated case‑law, in accordance with which Section 6(3)(a) of EUWA instructs courts and tribunals to decide cases before them.

However, on closer inspection, something about this outcome feels conceptually unstable. What the CJEU decides after all are only questions on the interpretation of EU law, nothing more and nothing less. The CJEU could not (and does not purport to) say anything about the meaning or effect of national law. The case in Bicknell turned on the definition of an “economic activity” in Regulation 3(2) of the domestic TUPE Regulations. However, the CJEU judgment in FENIN held, at [25], that “in Community competition law the definition of an ‘undertaking’ covers any entity engaged in an economic activity” (emphasis added). That the dispute turned on the domestic definition of an “economic activity”, while the CJEU commented on the EU law definition thereof, was a distinction without relevance in Bicknell, because at the material time the domestic law had to be given effect so to conform with EU law anyway, pursuant to the supremacy‑provision in Section 5(2) of EUWA, as applicable at the relevant time.

However, since 2024, that is no longer true: under Section 5(A1) of EUWA, the domestic regulations are now supreme, the meaning of the EU Directive is but an interpretative aid: admissible as part of an ordinary purposive interpretation of domestic law, but not binding or even conclusive as to its effect, due to Section 5(A1) of EUWA (see also E-Accounting Solutions Ltd (t/a Advancetrack) v Global Infosys Ltd (t/a GI Outsourcing) [2023] EWHC 2038 (Ch) at [13]).

This being so, there are reasonably two possible ways to think of assimilated case-law:

View 1: As the legislature has not made any relevant changes to the wording of Section 6(3)(a) EUWA as regards case law, it did evidently not intend to diminish its effect. Therefore, where a term in domestic legislation had to be conclusively interpreted and applied in accordance with CJEU case-law pre-2024, that remains the sole binding interpretation. That the CJEU case‑law as such originally only dealt with an EU law provision is nothing to the point, as its effect had already been incorporated for domestic purposes into the domestic legal order through the conforming-interpretation gateway. This view might find further support in the fact that under Section 7 of EUWA, it is not only the CJEU judgment itself which is assimilated, but also the “principles laid down by” it.

View 2: Conceptually, the effect of CJEU case law in the domestic legal order cannot go further than the effect of the EU legislation which it interprets. It may thus be determinative still where EU regulations have been retained under Section 3(1) EUWA; but as regards EU directives that were implemented in domestic enactments or regulations, its effect is merely the following: the pertinent CJEU judgment conclusively determines the meaning of the directive. But as the directive itself is just an interpretative aid for anything occurring since the beginning of 2024, the same must be true for the CJEU judgments attaching to that directive. The practical attraction of this approach is that it avoids the somewhat artificial severance of case law from its constituent directives which would occur if the former remained fully binding, but the latter would not. Such severance might, after all, give rise to rather arbitrary distinctions: where wording in a directive had been ambiguous, and the CJEU interpreted it, it would be binding. Where it was clear and not in need of interpretation, it would just be an external aid. That curious result is avoided if CJEU case law is likewise just an aid.

As Jack Williams has explained in his contribution, in Fry the Supreme Court applied an ordinary interpretation of provisions in domestic law which initially implemented an EU directive. CJEU case-law was treated as helpful background only, but without the Supreme Court considering itself bound by it pursuant to Section 6(3) of EUWA. That is curious; indeed it would be wrong, if one follows View 1 above. But if the Supreme Court shares View 2, then it would be an entirely plausible approach.

However, the issue was ultimately not tackled head on in Fry, and there is no express analysis of it in any other case. While it thus appears that View 2 might prevail in the Supreme Court, this is by no means clear. Calling assimilated case law a paper tiger just yet would therefore be premature. For now, it is rather Schrödinger’s cat, or Schrödinger’s tiger if you will: until a superior court open the box, it is powerful and weak at the same time.

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