The British House of Commons is the lower house of the Parliament of the United Kingdom. Parliament also includes the Sovereign and the upper house, the House of Lords; the House of Commons is the dominant branch. The House of Commons is a democratically elected body, consisting of 646 members, who are known as "Members of Parliament" or MPs. Members are elected by the first-past-the-post system of election, holding office until Parliament is dissolved (a maximum of five years). Each member is elected by, and represents, an electoral district known as a constituency. The House of Commons is the source of the vast majority of government ministers and every Prime Minister since 1902, with the very brief exception of Sir Alec Douglas-Home in 1963, has been drawn from it (Home did actually rule from the House of Commons, however, taking a seat in the House shortly after being chosen as Prime Minister).