The government is led by the Prime Minister, who selects all the remaining ministers. The prime minister and the other most senior ministers belong to the supreme decision-making committee, known as the Cabinet. The government ministers all sit in Parliament, and are accountable to it. The government is dependent on Parliament to make primary legislation, and since the Fixed-terms Parliaments Act 2011, general elections are held every five years to elect a new House of Commons, unless there is a successful vote of no confidence in the government or a two-thirds vote for a snap election (as was the case in 2017) in the House of Commons, in which case an election may be held sooner. After an election, the monarch (currently Queen Elizabeth II) selects as prime minister the leader of the party most likely to command the confidence of the House of Commons, usually by possessing a majority of MPs.
Under the uncodified British constitution, executive authority lies with the monarch, although this authority is exercised only by, or on the advice of, the prime minister and the cabinet. The Cabinet members advise the monarch as members of the Privy Council. They also exercise power directly as leaders of the Government Departments.
The current prime minister is Theresa May, who took office on 13 July 2016. She is the leader of the Conservative Party, which won a majority of seats in the House of Commons in the general election on 7 May 2015, when David Cameron was the party leader; although at the last general election she failed to secure a majority government. Prior to this, Cameron and the Conservatives led a coalition from 2010 to 2015 with the Liberal Democrats, in which Cameron was prime minister.
The United Kingdom is a constitutional monarchy in which the reigning monarch (that is, the King or Queen who is the Head of State at any given time) does not make any open political decisions. All political decisions are taken by the government and Parliament. This constitutional state of affairs is the result of a long history of constraining and reducing the political power of the monarch, beginning with the Magna Carta in 1215.