Politics of the United Kingdom of Great Britain and Northern Ireland take place in the framework of a constitutional monarchy in which the Monarch is head of state and the Prime Minister of the United Kingdom is the head of government. It is a pluriform multi-party system with a partial devolution of power in Scotland, Wales, and Northern Ireland. Executive power is exercised by the government. Legislative power is vested in both the government and the two chambers of Parliament, the House of Commons and the House of Lords. The judiciary is independent of the executive and the legislature.
Since the 1920s, the two largest political parties in British politics have been the Labour Party and Conservative Party. Though 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 to deliver a working majority in Parliament.
The Liberal Democrats, a party formed by the merger of the former Liberal Party and Social Democratic Party in 1988, are the third largest party in the British parliament. It seeks a reform of the electoral system to address the dominance of the two-party system. Though 'nationalist' (as opposed to 'unionist') tendencies have shifted over time in Scotland and Wales, with Plaid Cymru (the Party of Wales) in 1925, the Scottish National Party founded in 1934, Mebyon Kernow (the Party of Cornwall) in 1951, a serious political crisis threatening the integrity of the United Kingdom as a state has not occurred since the 1970s. Scotland, Wales, and Northern Ireland each possess a legislature and government alongside that of the United Kingdom. However, this increased autonomy and devolution of executive and legislative powers has not contributed to a reduction in support for independence from the United Kingdom, with the rise of new pro-independence parties. For example, the Scottish Green Party and the Scottish Socialist Party have gained popularity in recent years but have not significantly dented the parliamentary dominance on the three main parties. The constitution is uncodified, being made up of constitutional conventions, statutes and other elements.
This system of government, known as the Westminster system, has been adopted by other countries as well, such as Canada, India, Australia, New Zealand, Singapore, Malaysia and Jamaica, countries which made up part of the British Empire.