The United Kingdom is a parliamentary democracy based on universal adult suffrage. It is also a constitutional monarchy. Ministers govern in the name of the sovereign, who is the head of state and government, commander-in-chief of all the armed forces of the Crown and the supreme governor of the established Church of England. The constitution is unwritten, and relies on a combination of statutes, common law and convention.

The UK is a union of four countries: England, Scotland, Wales and Northern Ireland. The Crown dependencies (the Channel Islands and the Isle of Man) are largely self-governing with the UK responsible for their defence and international relations.

Parliament is bicameral, with an upper chamber, the House of Lords (89 hereditary peers, 678 life peers and 25 bishops in March 2011), and a lower chamber, the House of Commons (650 elected members). Elections to the lower chamber are held every five years.

The prime minister and cabinet lead the executive. The prime minister is appointed by the sovereign, and is usually the leader of the party who commands a majority in the House of Commons. The prime minister chooses and appoints the cabinet.

The UK Parliament enacts primary legislation, except where these matters have been devolved to the Scottish Parliament and Northern Ireland Assembly. The executive consists of the members of the cabinet, other ministers, government departments, local authorities, public corporations, regulatory bodies and other organisations subject to ministerial control.

Devolution changed the responsibilities of the Secretaries of State for Scotland, Wales and Northern Ireland, although they still retain UK Cabinet seats.

The judiciary determines common law and interprets statutes. The United Kingdom Supreme Court is the final court of appeal in civil matters for the whole of the UK, and in criminal matters everywhere except Scotland. In England and Wales, the High Court of Justice has three divisions, Chancery, Queen’s Bench and Family, which deal with certain more complex civil cases, while the county courts try the majority of civil cases. The Crown Court has jurisdiction in the most serious criminal cases providing trial by jury.