The United Kingdom is a unitary state with devolution that is governed within the framework of a parliamentary democracy under a constitutional monarchy in which the monarch, currently Charles III, King of the United Kingdom, is the head of state while the Prime Minister of the United Kingdom, Rishi Sunak, is the head of government. Executive power is exercised by the British government, on behalf of and by the consent of the monarch, and the devolved governments of Scotland, Wales and Northern Ireland. Legislative power is vested in the two chambers of the Parliament of the United Kingdom, the House of Commons and the House of Lords, as well as in the Scottish, Northern Irish and Welsh parliaments. The British political system is a two party system. Since the 1920s, the two dominant parties have been the Conservative Party and the Labour Party. Before the Labour Party rose in British politics, the Liberal Party was the other major political party, along with the Conservatives. While coalition and minority governments have been an occasional feature of parliamentary politics, the first-past-the-post electoral system used for general elections tends to maintain the dominance of these two parties, though each has in the past century relied upon a third party, such as the Liberal Democrats, to deliver a working majority in Parliament. A Conservative–Liberal Democrat coalition government held office from 2010 until 2015, the first coalition since 1945. The coalition ended following parliamentary elections on 7 May 2015, in which the Conservative Party won an outright majority of seats, 330 of the 650 seats in the House of Commons, while their coalition partners lost all but eight seats. With the partition of Ireland, Northern Ireland received home rule in 1920, though civil unrest meant direct rule was restored in 1972. Support for nationalist parties in Scotland and Wales led to proposals for devolution in the 1970s, though only in the 1990s did devolution happen. Today, Scotland, Wales and Northern Ireland each possess a legislature and executive, with devolution in Northern Ireland being conditional on participation in certain all-Ireland institutions. The British government remains responsible for non-devolved matters and, in the case of Northern Ireland, co-operates with the government of the Republic of Ireland. Devolution of executive and legislative powers may have contributed to increased support for independence in the constituent parts of the United Kingdom. The principal Scottish pro-independence party, the Scottish National Party,