The Parliament of the United Kingdom of Great Britain and Northern Ireland is the legislative body of that nation. Formally, Parliament consists of the monarch, the House of Commons, and the House of Lords. In common usage, however, the term refers to Commons and Lords only. Virtually all power rests with the House of Commons. The power exercised by Parliament is unlimited, making it in fact the sovereign of the nation.

The House of Commons has 659 elected members. The maximum period between elections is five years, but the actual timing of an election is usually decided by the prime minister. The total membership of the Lords is about 1,200, but the majority of the nation's peers take no active part in the proceedings of the house. Members of the Lords traditionally included hereditary peers, life peers, the 10 senior judges, the archbishops of Canterbury and York, and 24 bishops of the Church of England. (The right of the 758 hereditary peers to sit in the House of Lords was abolished in 1999.) Both houses, and especially the Commons, are organized along party lines. Normally the largest party in Commons forms the government, and the leading members of this party are appointed to senior ministerial positions (the cabinet). They must explain and defend their policies and acts to Commons.

All important legislation is introduced into Parliament by the government. The House of Lords no longer has the power to kill a piece of legislation. It can initiate amendments on bills (except money bills) and delay legislation.

Because the government usually has a majority in Commons, it can normally ensure that its major policies are accepted by Parliament. Party loyalty and discipline in Commons are strong. When the government, however, does not have an actual majority in Commons (because of third-party members), it must enlist enough support from minority members to get legislation passed. When such coalitions fail on an important vote, the government falls. The prime minister and cabinet resign, and if no other party leader is able to form a government, Parliament is dissolved and a new election is called.

Parliament evolved from the Curia Regis, or Great Council of the Realm, which began in the Middle Ages as an advisory body to the monarch. Originally it comprised the great landholders, the chief nobles, and the church prelates. Beginning in the 13th century the monarch occasionally would call up representatives of the other classes, mainly the knights, the lower clergy, and the burgesses. The two bodies met separately, however, and eventually evolved into, respectively, the House of Lords and the House of Commons.

Parliament's history is one of long competition with the monarchy, and eventual supremacy. Important milestones in that competition include the early Commons'assertion of control over grants of revenue to the monarch; the English Civil War, during which Parliament ordered the beheading of the king; the Glorious Revolution of 1688, during which Parliament succeeded in establishing its sovereignty over the crown; the growing dependence of the prime minister on Parliament (instead of on the monarch) during the 18th century; the great reforms of the 19th century, which extended suffrage to most of the adult male population and established the secret ballot; the Parliament Act of 1911, which abolished the veto power of the Lords; and the Representation of the People Acts of 1918, 1928, 1948, and 1969, which extended the suffrage to women, established the principle of one person one vote, and lowered the voting age from 21 to 18.

In January 2000, after the exclusion of the hereditary peers, the Wakeham Royal Commission issued a plan for the reform of the House of Lords, calling for a chamber of 550 members, between 20% and 40% of whom would be elected by regional proportional representation. The remainder would be appointed by an independent commission. A certain number of seats would be reserved for women and ethnic minorities. A "spiritual bench" would have 16 seats for the Church of England, 10 seats for other Christian churches, and 5 for non-Christian religions. The plan was widely criticized as not going far enough in the direction of democratizing the Lords. In April 2001 the House of Lords appointments commission named the first 15 "people's peers," chosen from more than 3,000 applicants.

Bibliography: Hart, Jenifer, Proportional Representation (1992); Hexter, J. H., ed., Parliament and Liberty: From the Reign of Elizabeth to the English Civil war (1992); Lang, Sean, Parliamentary Reform, 1785–1928 (1998); Norton, Philip, and Wood, David, Back from Westminster: British Members of Parliament and Their Constituents (1993); Pollard, A. F., The Evolution of Parliament, 2d ed. (1926; repr. 1964); Punnett, R. M., Front Bench Opposition (1973); Richards, Peter G., The Backbenchers (1972); Robertson, David, Judicial Discretion in the House of Lords (1998); Roskell, J. S., Parliament and Politics in Late Medieval England, 3 vols. (1985); Rush, Michael, Parliament and the Public, 2d ed. (1986); Silk, Paul, and Walters, Rhodri, How Parliament Works, 4th ed. (1998); Tomkins, Adam, The Constitution after Scott: Government Unwrapped (1998).