Supreme Court of the United Kingdom

The constitution of the United Kingdom comprises the written and unwritten arrangements that establish the United Kingdom of Great Britain and Northern Ireland as a political body. Unlike in most countries, no official attempt has been made to codify such arrangements into a single document, thus it is known as an uncodified constitution. This enables the constitution to be easily changed as no provisions are formally entrenched.

The Supreme Court of the United Kingdom and its predecessor, the Appellate Committee of the House of Lords, have recognised and affirmed constitutional principles such as parliamentary sovereignty, the rule of law, democracy, and upholding international law. It also recognises that some Acts of Parliament have special constitutional status. These include the Magna Carta, which in 1215 required the King to call a "common counsel" (now called Parliament) to represent the people, to hold courts in a fixed place, to guarantee fair trials, to guarantee free movement of people, to free the church from the state, and to guarantee rights of "common" people to use the land. After the Glorious Revolution, the Bill of Rights 1689 and the Claim of Right Act 1689 cemented Parliament's position as the supreme law-making body, and said that the "election of members of Parliament ought to be free". The Treaty of Union in 1706 and the Acts of Union 1707 united the Kingdoms of England, Wales and Scotland, the Acts of Union 1800 joined Ireland, but the Irish Free State separated after the Anglo-Irish Treaty in 1922, leaving Northern Ireland within the UK. After struggles for universal suffrage, the UK guaranteed every adult citizen over 21 years the equal right to vote in the Representation of the People (Equal Franchise) Act 1928. After World War II, the UK became a founding member of the Council of Europe to uphold human rights, and the United Nations to guarantee international peace and security. The UK was a member of the European Union, joining its predecessor in 1973, but left in 2020. The UK is also a founding member of the International Labour Organization and the World Trade Organization to participate in regulating the global economy.

The Courts of England and Wales, supported administratively by His Majesty's Courts and Tribunals Service, are the civil and criminal courts responsible for the administration of justice in England and Wales.

Except in constitutional matters, committed to the Supreme Court of the United Kingdom, the United Kingdom does not generally have a single unified legal system—England and Wales have one system, Scotland another, and Northern Ireland a third. There are additional exceptions to this rule; for example, in immigration law, the Asylum and Immigration Tribunal's jurisdiction covers the whole of the United Kingdom, while in employment law, there is a single system of employment tribunals for England, Wales, and Scotland but not Northern Ireland. Additionally, the Military Court Service has jurisdiction over all members of the armed forces of the United Kingdom in relation to offences against military law.

The courts of Scotland (Scottish Gaelic: Cùirtean na h-Alba) are responsible for administration of justice in Scotland, under statutory, common law and equitable provisions within Scots law. The courts are presided over by the judiciary of Scotland, who are the various judicial office holders responsible for issuing judgments, ensuring fair trials, and deciding on sentencing. The Court of Session is the supreme civil court of Scotland, subject to appeals to the Supreme Court of the United Kingdom, and the High Court of Justiciary is the supreme criminal court, which is only subject to the authority of the Supreme Court of the United Kingdom on devolution issues and human rights compatibility issues.

The judiciary of Scotland, except the Lord Lyon King of Arms, are united under the leadership and authority of the Lord President and Lord Justice General, who is the president of the Court of Session and High Court of Justiciary. The Court of Session has the authority, under the Courts Reform (Scotland) Act 2014, to regulate civil procedure through passing subordinate legislation knows as Acts of Sederunt, and the High Court of Justiciary has the authority to regulate criminal procedure through passing Acts of Adjournal. Both Acts of Sederunt and Acts of Adjournal have the capacity to amend primary legislation where it deals with civil or criminal procedure respectively.

In the United Kingdom, life peers are appointed members of the peerage whose titles cannot be inherited, in contrast to hereditary peers. Life peers are appointed by the monarch on the advice of the prime minister. With the exception of the Dukedom of Edinburgh awarded for life to Prince Edward in 2023, all life peerages conferred since 2009 have been created under the Life Peerages Act 1958 with the rank of baron. Such peerages entitle (or perhaps obligate) the holder to sit and vote in the House of Lords (so long as they meet qualifications such as age and citizenship). Prior to 2009, life peers of baronial rank could also be created under the Appellate Jurisdiction Act 1876 for senior judges, referred to as Law Lords, with functions then taken over by the new Supreme Court.

The legitimate children of a life peer appointed under the Life Peerages Act 1958 are entitled to style themselves with the prefix "The Honourable", although they cannot inherit the peerage.

Justices of the Supreme Court of the United Kingdom are the judges of the Supreme Court of the United Kingdom other than the president and the deputy president of the court. The Supreme Court is the highest court of the United Kingdom for all civil cases, and for criminal cases from the jurisdictions of England and Wales and Northern Ireland. Judges are appointed by the British monarch on the advice of the prime minister, who receives recommendations from a selection commission.

The number of judges is set by section 23(2) of the Constitutional Reform Act 2005, which established the Supreme Court, but may be increased by Order in Council under section 23(3). There are currently twelve positions on the court: the president, the deputy president, and ten justices. Judges of the Court who are not already peers are granted the judicial courtesy title of Lord or Lady.

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.

On 29 March 2017, the United Kingdom (UK) invoked Article 50 of the Treaty on European Union which began the member state's withdrawal, commonly known as Brexit, from the European Union (EU). In compliance with the treaty, the UK gave formal notice to the European Council of its intention to withdraw from the EU to allow withdrawal negotiations to begin.

The process of leaving the EU was begun after a referendum held in June 2016 at which 52% of the votes were in favour of UK withdrawal. In October 2016, the UK prime minister, Theresa May, announced that Article 50 would be invoked by "the first quarter of 2017". On 24 January 2017 the Supreme Court ruled in Miller I that the process could not be initiated without an authorising Act of Parliament, and unanimously ruled against the Scottish Government's claim in respect of devolution. Consequently, the European Union (Notification of Withdrawal) Act 2017 empowering the prime minister to invoke Article 50 was enacted in March 2017.