R (Factortame Ltd) v Secretary of State for Transport (No 2) [1991] 1 AC 603
Factortame is the high-water mark of EU law supremacy in UK courts. Spanish fishermen challenged Part II of the Merchant Shipping Act 1988, which imposed nationality and residence conditions on the registration of fishing vessels, arguing that it breached EU law on freedom of establishment. The House of Lords referred the question to the ECJ, which held that national courts must set aside national law preventing the full effectiveness of EU law. The Lords then granted an interim injunction against the Crown and ultimately disapplied the 1988 Act.
Lord Bridge's judgment is constitutionally pivotal. He emphasised that the outcome was 'not in any way novel' given Parliament's acceptance of EU membership. The 1972 Act had 'precisely defined' the limits of parliamentary sovereignty for the duration of membership. Crucially, this was not judicial activism but judicial obedience to Parliament's own instruction.
Thoburn v Sunderland City Council [2002] EWHC 195 (Admin)
Laws LJ's judgment introduced the concept of 'constitutional statutes', which cannot be impliedly repealed. He identified the ECA 1972 as a constitutional statute because it conditions the relationship between the UK and EU legal orders. An ordinary statute (Weights and Measures Act 1985) could not impliedly repeal the 1972 Act; only express words or necessary implication would suffice. This doctrine reconciles supremacy with continuing sovereignty: Parliament remains sovereign because it can expressly repeal the ECA 1972, but in the absence of such repeal, EU law prevails. The judgment, though only at first instance, has been widely cited and adopted in later cases, including HS2 [2014] UKSC 3.
R (Miller) v Secretary of State for Exiting the European Union [2017] UKSC 5 (Miller No 1)
The Supreme Court held that the Crown could not trigger Article 50 TEU using prerogative powers; an Act of Parliament was required. The reasoning turned on constitutional fundamentals. Withdrawal would inevitably result in a change in domestic law (the loss of EU-derived rights), and the prerogative cannot be used to change statute law. The 1972 Act had conferred rights that would be removed by withdrawal, and only Parliament could authorise that removal.
The Court rejected the government's argument that the rights in question were contingent on the UK's continued membership and thus derived from treaty, not statute. Lord Neuberger PSC, delivering the lead judgment, held that the 1972 Act was the source of rights in domestic law. Ministers could not, by exercise of prerogative treaty-making power, remove what Parliament had enacted. The judgment reaffirmed the core separation-of-powers principle and the Diceyan rule that the Crown acts under law, not above it.
R (Miller) v The Prime Minister; Cherry v Advocate General for Scotland [2019] UKSC 41 (Miller No 2/Cherry)
This case concerned the Prime Minister's prorogation of Parliament in September 2019 for five weeks during the Brexit process. The Supreme Court unanimously held the prorogation unlawful. Lady Hale PSC, delivering the judgment, held that the prorogation had the effect of frustrating or preventing Parliament's ability to carry out its constitutional functions without reasonable justification. The court identified justiciability (the question was one of law), the legal limits on the prerogative (it cannot be used to undermine parliamentary sovereignty or responsible government), and the absence of any reasonable justification for the length of prorogation.
While Miller No 2 was not formally an 'EU law' case, it arose directly from Brexit politics and demonstrated judicial willingness to police the boundaries of executive power even in a politically charged context. It affirmed that parliamentary sovereignty includes the effective ability of Parliament to sit and legislate, and that the executive is subordinate to law.
R (on the application of Privacy International) v Investigatory Powers Tribunal [2019] UKSC 22
Though primarily a case on ouster clauses, Lord Carnwath's judgment (concurring) suggested that parliamentary sovereignty itself might be subject to judicial limitation where fundamental rule-of-law principles are at stake. This controversial dictum—that 'the courts have the last word on the interpretation of the law'—was expressly disapproved obiter by Lords Reed and Hodge in Privacy International. The debate echoes earlier dicta in Jackson v Attorney General [2005] UKHL 56, where Lords Steyn and Hope suggested that there might be constitutional limits on what Parliament can do. These statements remain controversial and have not been adopted by a majority, but they indicate ongoing judicial reflection on the scope of sovereignty in an era of constitutional stress.
European Union (Withdrawal) Act 2018 Reference [2018] UKSC (not formally reported as a case)
This was not a litigated case but an important constitutional moment: the passage of the 2018 Act through Parliament demonstrated the legislative sovereignty principle in action. Parliament could, and did, repeal the ECA 1972, terminate EU law supremacy, and redesign the domestic legal order. The political difficulty and legislative complexity should not obscure the legal simplicity: no court, no external body, and no constitutional limit prevented Parliament from legislating for withdrawal. This empirical fact vindicates the orthodox sovereignty account.