Parliamentary sovereignty

If the UK constitution has a cornerstone, it is parliamentary sovereignty. The doctrine holds that Parliament is the supreme legal authority in the United Kingdom — that it can make or unmake any law, and that no other body can override what it has enacted. Simple to state, the principle has profound consequences for how Britain is governed, and in the modern era it has come under real strain from devolution, the courts and the legacy of EU membership. Understanding both the doctrine and these tensions is essential to understanding the British constitution.

Dicey’s doctrine

The classic statement comes from the constitutional lawyer A.V. Dicey, writing in 1885. He described parliamentary sovereignty as the dominant characteristic of Britain’s political institutions, and broke it into three propositions:

• Parliament can make or unmake any law whatever. There is no legal limit on the subject matter of legislation; Parliament can legislate on any topic.
• No Parliament can bind its successors. One Parliament cannot pass a law that a later Parliament is unable to change.
• No body can override or set aside an Act of Parliament. No person or institution, including the courts, has a legal right to invalidate primary legislation.

The first proposition means there is no area of life beyond Parliament’s legal reach. The courts must give effect to a validly passed Act of Parliament; unlike the supreme courts of many countries, British courts have no power to declare a statute unconstitutional and strike it down.

The second is more subtle but equally important. Because each Parliament is equally sovereign, no Parliament can entrench its decisions against a future one. If it could, the earlier Parliament would be supreme over the later — contradicting the idea that every Parliament holds the same supreme authority.

The absence of entrenchment

A direct consequence is that the UK has no fully entrenched laws. Entrenchment means protecting certain laws so that they can only be changed by a special procedure — a supermajority, a referendum, or a constitutional amendment process. In many countries with codified constitutions, fundamental provisions are protected in exactly this way.

In the UK, by contrast, even Acts of the greatest constitutional importance — on human rights, devolution or the union itself — have, in strict legal terms, no higher status than any other statute. They can be amended or repealed by an ordinary majority in a later Parliament. This gives the constitution great flexibility, but it also means that rights and constitutional arrangements rest, ultimately, on the restraint of Parliament rather than on legal entrenchment.

Modern tensions

Although the doctrine remains the orthodox foundation of the constitution, several modern developments have created tensions with it.

The courts and the Human Rights Act. The Human Rights Act 1998 requires courts to interpret legislation compatibly with the European Convention on Human Rights where possible. Where a statute cannot be reconciled, a court may issue a declaration of incompatibility. Crucially, this does not strike the law down: Parliament remains legally free to leave it unchanged. The mechanism was deliberately designed to give effect to rights while preserving sovereignty, but it has sharpened debate about the proper balance between Parliament and the judiciary.

Devolution. Devolution has transferred wide-ranging powers to the Scottish Parliament, the Senedd in Wales and the Northern Ireland Assembly. In strict law, Westminster remains sovereign and could alter or even abolish these arrangements. In practice, however, the Sewel convention provides that the UK Parliament will not normally legislate on devolved matters without the consent of the relevant devolved legislature. Because this is a political convention rather than a legally enforceable rule, legal sovereignty is preserved — yet political reality increasingly constrains how, and whether, Westminster uses it.

EU membership and its end. While the UK was a member of the European Union, EU law took precedence in many areas, which some regarded as a qualification of sovereignty. Defenders of the doctrine pointed out that Parliament had voluntarily enacted this arrangement and could repeal it — which is, in the end, what happened. The European Union (Withdrawal) Act 2018 and subsequent legislation ended the supremacy of EU law and converted much of it into “retained” (later “assimilated”) UK law. That body of law now has the status of ordinary domestic legislation, which Parliament is free to amend or repeal — a vivid illustration of sovereignty reasserting itself after Brexit.

Legal authority versus political reality

A final distinction is essential. Parliamentary sovereignty describes Parliament’s legal authority, which is unlimited — not its freedom of action, which is not. In practice Parliament is constrained by elections, public opinion, practicality, international agreements and constitutional conventions. There are many laws Parliament could pass in strict law but would never pass in reality.

Sovereignty, then, is best understood as a statement about where supreme legal power resides, not a claim that Parliament can or will do anything at all. The modern tensions do not so much abolish the doctrine as complicate it: legally Parliament remains supreme, but the political and constitutional landscape in which it exercises that supremacy has become markedly more layered than in Dicey’s day.