Constitution of the United Kingdom

The United Kingdom's constitution is the collection of written and unwritten rules that define how the country is governed. Unlike most nations, it has never been gathered into a single document, making it an uncodified constitution. This lack of formal entrenchment means it can be altered relatively easily.

The Supreme Court (and its predecessor, the House of Lords' Appellate Committee) has identified key constitutional principles, including parliamentary sovereignty, the rule of law, democracy, and respect for international law. Certain Acts of Parliament are considered to have special constitutional status. Among these is Magna Carta (1215), which required the monarch to summon a "common counsel" (now Parliament), hold courts in a fixed place, guarantee fair trials, allow free movement, separate the church from the state, and protect common people's rights to use land. The Laws in Wales Acts (1535 and 1542) integrated Wales into England after its conquest. Following the Glorious Revolution, the Bill of Rights (1689) and the Claim of Right Act (1689) established Parliament as the supreme law-making body and declared that elections for Parliament should be free. The Treaty of Union (1706) and Acts of Union (1707) united England and Scotland; the Acts of Union (1800) joined Ireland, though the Irish Free State separated in 1922, leaving only Northern Ireland in the UK. After campaigns for universal suffrage, the Representation of the People (Equal Franchise) Act 1928 gave every adult citizen over 21 an equal right to vote. After World War II, the UK helped found the Council of Europe to protect human rights and the United Nations for international peace and security. It joined the European Union's predecessor in 1973 and left in 2020. The UK is also a founding member of the International Labour Organization and the World Trade Organization.

The main institutions are Parliament, the judiciary, the executive, and regional and local governments (including devolved bodies in Scotland, Wales, and Northern Ireland). Parliament is the supreme law-making body, representing the people. The House of Commons is elected by democratic vote across 650 constituencies. The House of Lords is mostly appointed by cross-party groups from the Commons and can delay, but not block, legislation. To create an Act of Parliament—the highest form of law—both Houses must read, amend, or approve a bill three times, and the monarch must give consent. The judiciary interprets laws from Acts of Parliament and develops law from previous court cases. The highest court is the twelve-member Supreme Court, which hears appeals from the Courts of Appeal in England, Wales, and Northern Ireland, or from Scotland's Court of Session. UK courts cannot declare Acts of Parliament unconstitutional or invalid, but they can state that an Act is incompatible with the European Convention on Human Rights. They can also rule on whether executive actions are lawful. The executive is led by the prime minister, who must keep the confidence of a majority in the House of Commons. The prime minister appoints a cabinet of ministers who run executive departments (staffed by civil servants), such as the Department of Health and Social Care (which runs the NHS) or the Department for Education (which funds schools and universities).

The monarch, in their public role as the Crown, represents the state. Laws can only be made by or with the Crown's authority in Parliament; all judges sit in the Crown's place, and all ministers act in its name. The monarch is mostly a ceremonial figure and has not refused assent to a law since the Scottish Militia Bill in 1708. The monarch is bound by constitutional convention.

Beyond the supreme UK Parliament, devolution has granted legislative powers to the Scottish Parliament, the Senedd (formerly the National Assembly for Wales), and the Northern Ireland Assembly. In England, the Greater London Authority and combined authorities have oversight and general responsibilities. Ultimate authority remains with the UK Parliament, which has passed laws like the United Kingdom Internal Markets Act 2020.

Most constitutional questions arise in judicial review cases, which decide whether public bodies' decisions or actions are lawful. Every public body must act according to the law set out in Acts of Parliament and court decisions. Under the Human Rights Act 1998, courts can review government action to check if it follows the statutory duty for all public authorities to comply with the European Convention on Human Rights. Convention rights include the rights to life, liberty (against arbitrary arrest or detention), freedom from torture and forced labour, a fair trial, privacy (against unlawful surveillance), freedom of expression, conscience, and religion, respect for private life, freedom of association (including joining trade unions), and freedom of assembly and protest.