Parliament is the supreme legislative authority and consists of three separate elements: the Sovereign, the House of Lords and the elected House of Commons. Over the centuries the balance between the three parts of the legislature has changed, so that the Queen's role is now only formal and the House of Commons has gained supremacy over the House of Lords.
The House of Commons is a popular assembly elected by almost universal adult suffrage. There are 659 Members of Parliament (MPs) — each member representing one of the 659 geographical areas (constituencies) into which the country is divided for electoral purposes. If an MP dies, resigns or is made a peer, a by-election is held in that constituency to elect a new MP. Leaders of the Government and Opposition sit on the front benches of the Commons, with their supporters (back-benchers) behind them. The House is presided over by the Speaker.
The main function of the House of Commons is to legislate, but the strong party system in Britain has meant that the initiative in government lies not with Parliament but with the Government (most Bills are introduced by the Government, although they may also be introduced by individual MPs) and party members almost automatically pass whatever is put before them by their party.
The House of Lords, which is presided over by the Lord Chancellor, is probably the only upper House in the democratic world whose members are not elected. It is made up of the Lords Spiritual and the Lords Temporal; the former consist of the representatives of the Church of England (the Archbishops of York and Canterbury and 25 bishops). The House of Lords can revise Bills sent to it by the House of Commons but it can only delay a Bill from becoming law for a maximum of 12 months.