The United Kingdom constitutional law concerns the governance of the United Kingdom of Great Britain and Northern Ireland. With the oldest continuous political system on Earth, the British constitution is not contained in a single code but principles have emerged over centuries from common law statute, case law, political conventions and social consensus. In 1215, Magna Carta required the King to call "common counsel" or Parliament, hold courts in a fixed place, guarantee fair trials, guarantee free movement of people, free the church from the state, and it enshrined the rights of "common" people to use the land. After the English Civil War and the Glorious Revolution 1688, Parliament won supremacy over the monarch, the church and the courts, and the Bill of Rights 1689 recorded that the "election of members of Parliament ought to be free". The Act of Union 1707 unified England, Wales and Scotland, while Ireland was joined in 1800, but the Republic of Ireland formally separated between 1916 and 1921 through bitter armed conflict. By the Representation of the People (Equal Franchise) Act 1928, almost every adult man and woman was finally entitled to vote for Parliament. The UK was a founding member of the International Labour Organization (ILO), the United Nations, the Commonwealth, the Council of Europe, and the World Trade Organization (WTO).
The constitutional principles of parliamentary sovereignty, the rule of law, democracy and internationalism guide the UK's modern political system. The central institutions of modern government are Parliament, the judiciary, the executive, the civil service and public bodies which implement policies, and regional and local governments. Parliament is composed of the House of Commons, elected by voter constituencies, and the House of Lords which is mostly appointed on the recommendation of cross-political party groups. To make a new Act of Parliament, the highest form of law, both Houses must read, amend, or approve proposed legislation three times. The judiciary is headed by a twelve-member Supreme Court. Underneath are the Court of Appeal for England and Wales, the Court of Appeal in Northern Ireland, and the Court of Session for Scotland. Below these lie a system of high courts, Crown courts, or tribunals depending on the subject in the case. Courts interpret statutes, progress the common law and principles of equity, and can control the discretion of the executive. While the courts may interpret the law, they have no power to declare an Act of Parliament unconstitutional. The executive is headed by the Prime Minister, who must command a majority in the House of Commons. The Prime Minister appoints a cabinet of people who lead each department, and form His Majesty's Government. The King himself is a ceremonial figurehead, who gives royal assent to new laws. By constitutional convention, the monarch does not usurp the democratic process and has not refused royal assent since the Scottish Militia Bill in 1708. Beyond the Parliament and cabinet, a civil service and a large number of public bodies, from the Department of Education to the National Health Service, deliver public services that implement the law and fulfil political, economic and social rights.
