The parliament is bicameral, with an upper house, the House of Lords, and a lower house, the House of Commons. The Queen is the third component of the legislature. The House of Lords includes two different types of members: the Lords Spiritual (the senior bishops of the Church of England) and the Lords Temporal (members of the Peerage) whose members are not elected by the population at large, but are appointed by the Sovereign on advice of the Prime Minister.
Prior to the opening of the Supreme Court in October 2009 the House of Lords also performed a judicial role through the Law Lords. The House of Commons is a democratically elected chamber with elections to it held at least every five years. The two Houses meet in separate chambers in the Palace of Westminster (commonly known as the Houses of Parliament), in London. By constitutional convention, all government ministers, including the Prime Minister, are members of the House of Commons or, less often, the House of Lords, and are thereby accountable to the respective branches of the legislature.
The Parliament of Great Britain was formed in 1707 following the ratification of the Treaty of Union by both the Parliament of England and Parliament of Scotland passing Acts of Union. However, in practice the parliament was a continuation of the English parliament with the addition of Scottish MPs and peers. Parliament was further enlarged by the ratification by the Parliament of Great Britain and the Parliament of Ireland of the Act of Union (1800), which abolished the Irish Parliament; this added 100 Irish members to the Commons and 32 to the Lords to create the Parliament of the United Kingdom of Great Britain and Ireland. It has been called "the mother of parliaments", its democratic institutions having set the standards for many democracies throughout the world, and the United Kingdom parliament is the largest Anglophone legislative body in the world.
In theory, supreme legislative power is vested in the Queen-in-Parliament; in practice in modern times, real power is vested in the House of Commons, as the Sovereign generally acts on the advice of the Prime Minister, and the powers of the House of Lords have been limited.