The first signs of divergence between the UK and EU legal systems are starting to emerge in cases based on the proper approach to retained EU law.
In Open Rights Group & Anor, R (On the Application Of) v Secretary of State for the Home Department & Anor  EWCA Civ 1573, the Court of Appeal considered how to respond when asked to exercise a power to delay the implementation of dominant rules of retained EU law in the context of data protection rules.
The complicating factor was that this power had previously been exercisable only by the CJEU.
The Court had to consider whether it could assume that power for itself or whether it was forced to hold that the power had essentially vanished after the ending of the CJEU’s jurisdiction with Brexit.
Warby LJ gave a comprehensive summary of the Court’s position following the end of the Implementation Period:
(1) A UK court must now decide any question as to the validity, meaning or effect of any retained EU law for itself: it is no longer possible to refer any matter to the CJEU: EUWA s 6(1)(b).
(2) But the general rule is that the court must decide any such question in accordance with any retained case law and any retained general principles of EU law that are relevant: EUWA s 6(3). “Retained EU case law” and “retained general principles” mean principles laid down and decisions made by the CJEU before IP completion day.
(3) When it comes to principles laid down or decisions made by the CJEU after IP completion day, the court is not bound (EUWA s 6(1)) but “may have regard” to them (EUWA s 6(2)).
(4) The position is different in a “relevant court”, which includes the Court of Appeal. Subject to an exception that does not apply here, a relevant court is not absolutely bound by any retained EU case law: EUWA s 6(4)(ba) and Regulations 1 and 4. It can depart from that law; but the test to be applied in deciding whether to do so is “the same test as the Supreme Court would apply in deciding whether to depart from the case law of the Supreme Court”: EUWA 6(5A)(c) and Regulation 5.
(5) The test the Supreme Court applies is the one laid down by the House of Lords in its Practice Statement  1 WLR 1234, when Lord Gardiner LC said this:
“Their Lordships regard the use of precedent as an indispensable foundation upon which to decide what is the law and its application to individual cases. It provides at least some degree of certainty upon which individuals can rely in the conduct of their affairs, as well as a basis for orderly development of legal rules.
Their Lordships nevertheless recognise that too rigid adherence to precedent may lead to injustice in a particular case and also unduly restrict the proper development of the law. They propose, therefore, to modify their present practice and, while treating former decisions of this House as normally binding, to depart from a previous decision when it appears right to do so.
In this connection they will bear in mind the danger of disturbing retrospectively the basis on which contracts, settlements of property and fiscal arrangements have been entered into and also the especial need for certainty as to the criminal law.
This announcement is not intended to affect the use of precedent elsewhere than in this House.”
Warby LJ rejected the suggestion that the power to delay the implementation of EU rules had simply been lost:
This would be an unduly mechanistic and literal approach, tending to subvert rather than promote the legal policy that underlies this aspect of the CJEU jurisprudence.
It was important to recognise that the English and EU legal systems were fundamentally different in terms of structure:
The EU structure has no analogue within our domestic system of courts and tribunals. We have different means of ensuring the uniform and consistent interpretation and application of the law. In our system, as a rule, courts and tribunals at all levels are duty bound to decide legal issues on which there is no precedent that binds them. Our Supreme Court is a final court of appeal, not a court to which inferior courts and tribunals refer a question without first deciding it.
This meant that there was in theory no danger of departing from retained EU law when allowing an English court to employ a power formerly reserved only to the CJEU:
In such a system, there is no need nor any reason to adopt the principle that reserves the power to suspend to the supreme judicial authority. Indeed, it seems to me that the second element of the CJEU decisions is incapable of application here. On this analysis, there is no question of departing from retained EU law; the principle in question has not been retained because it cannot be translated. And on this analysis any first instance court or tribunal can, in principle, suspend relief.
It followed that the court could exercise the power:
For these reasons, I would hold that this Court has the power identified in the CJEU jurisprudence: to delay or suspend the implementation of a dominant rule of (retained) EU law, and the consequent disapplication of an inconsistent domestic provision.