Parliamentary Sovereignty

Parliamentary sovereignty is the foundational principle of the UK constitution. A.V. Dicey identified three elements: (1) Parliament can make or unmake any law on any subject, (2) no Parliament can bind its successors (or be bound by its predecessors), and (3) no body can question the validity of an Act of Parliament.

The principle was affirmed in Edinburgh and Dalkeith Railway v Wauchope (1842) 8 Cl & F 710 and Pickin v British Railways Board [1974] AC 765, where the House of Lords held that courts cannot inquire into the internal proceedings of Parliament to question the validity of an Act (the enrolled act rule).

The doctrine of implied repeal holds that where two statutes conflict, the later statute prevails and impliedly repeals the earlier one to the extent of the inconsistency. This is a corollary of the rule that no Parliament can bind its successors.

However, in Thoburn v Sunderland City Council [2002] EWHC 195 (Admin) (the "Metric Martyrs" case), Laws LJ introduced the concept of "constitutional statutes" — statutes of fundamental constitutional importance (such as Magna Carta, the Bill of Rights 1689, the European Communities Act 1972, and the Human Rights Act 1998) that cannot be impliedly repealed. They can only be repealed by express words or by a later statute that makes the repeal "crystal clear."

The European Communities Act 1972 (ECA 1972) gave effect to EU law in the UK. Section 2(1) provided that EU law was directly applicable, and s.2(4) required UK courts to construe domestic legislation consistently with EU law. In R v Secretary of State for Transport, ex parte Factortame (No 2) [1991] 1 AC 603, the House of Lords disapplied provisions of the Merchant Shipping Act 1988 that conflicted with EU law.

The Supreme Court in R (Miller) v Secretary of State for Exiting the EU [2017] UKSC 5 held that the ECA 1972 was a constitutional statute that could not be impliedly repealed by the exercise of prerogative power. An Act of Parliament was required to authorise notification under Article 50 TEU.

The European Union (Withdrawal) Act 2018 repealed the ECA 1972 and converted existing EU law into domestic law ("retained EU law"). The Retained EU Law (Revocation and Reform) Act 2023 further reformed the status of retained EU law, removing its special status and treating it as ordinary domestic legislation.

The Human Rights Act 1998 (HRA) incorporates the European Convention on Human Rights into domestic law. Under s.3, courts must read and give effect to legislation "so far as it is possible to do so" in a way that is compatible with Convention rights. Under s.4, if a court cannot interpret legislation compatibly, it may issue a declaration of incompatibility — but this does not affect the validity of the legislation.

The HRA preserves parliamentary sovereignty because: (1) s.3 interpretation is limited to what is "possible" — courts cannot rewrite legislation (Ghaidan v Godin-Mendoza [2004] 2 AC 557), and (2) a declaration of incompatibility under s.4 does not strike down the legislation — Parliament retains the choice of whether to amend it (Bellinger v Bellinger [2003] 2 AC 467).