UK parliamentary government based on the party system has evolved only during the past 100 years. Although the 18th-century terms "Whig" and "Tory" indicated certain political leanings, there was no clear-cut division in Parliament and no comprehensive party organization. Not until the 19th-century Reform Acts enfranchised millions of new voters did the modern party system develop. The British party system is based on the assumption that there are at least two parties in the Commons, each with a sufficiently united following to be able to form an alternative government at any time. This assumption is recognized in the fact that the largest minority party is officially designated as Her Majesty's Opposition; its leader, who designates a "shadow government," is paid a salary from public funds.
The main political parties represented in Parliament today are the Labor Party, the Conservative Party, and the Liberal Democrats (a coalition of the Liberal and Social Democratic parties, which voted in favor of a formal merger in 1988). From time to time during the past 50 years, other parties have arisen or have splintered off from the main groups, only to disappear or to become reabsorbed. Thus, the Fascists, who were of some significance before World War II, no longer put up candidates for elections, and the British Communist Party has not elected a candidate to Parliament since 1950.
Since World War I, the Labor Party has replaced the Liberal Party, a major force during the late 19th century, as the official opposition to a Conservative government. Founded in 1900 as the political arm of the already powerful trade union movement, the Labor Party was until 1918 a federation of trade unions and socialist groups and had no individual members. Today, its constituent associations consist of affiliated organizations (such as trade unions, cooperative societies, branches of socialist societies, and trade councils), as well as individual members organized into wards. Its program calls for public ownership of the means of production, improvement of the social and economic conditions of the people, defense of human rights, cooperation with labor and socialist organizations of other countries, and peaceful adjustment of international disputes. Between the world wars, it established two short-lived Labor governments while still a minority party, and then joined Churchill's coalition government in World War II. Returned to power with a huge majority in 1945, Labor instituted a program of full employment through planned production; established social services to provide adequate medical care, old age care, nutrition, and educational opportunities for all; began the nationalization of basic industries; and started to disband the empire by granting independence to India, Pakistan, Ceylon (now Sri Lanka), and Burma (Myanmar).
If the rapid rise of the Labor Party has been an outstanding feature of 20th-century British politics, the continuing vitality and adaptability of the Conservative Party, successor of the 18th-century Tories, has been no less remarkable. In foreign affairs, there has been little difference between the parties since World War II. Both have generally been firm allies of the United States, and both are pledged to the maintenance of NATO. The two parties have also been in general agreement about the country's social and economic needs. They differ mainly on the degree of state control to be applied to industry and commerce and on practical methods of application. Conservative emphasis is on free enterprise, individual initiative, and restraining the power of the unions. Even on these matters, however, pragmatism is the norm. In office, the Conservatives have let stand much of Labor's social program, and Labor, during Britain's economic difficulties in the late 1970s, imposed its own policy of wage restraints.
After World War II, Labor was in power during 1945–51, 1964–70, 1974–79, and since 1997; the Conservatives have held office during 1951–64, 1970–74, and 1979–97. Scottish National Party members were decisive in the fall of the Labor government in March 1979, after Labor was unable to enact its program for limited home rule (including elected legislatures) in Scotland and Wales. In elections of 3 May 1979, after a campaign fought mainly on economic grounds, Conservatives won 339 seats, with 43.9% of the vote, to Labor's 268 seats, with 36.9%, and Margaret Thatcher replaced James Callaghan as prime minister. Amid growing dissension, the Labor Party moved leftward in the early 1980s and broke with the Conservatives over defense policy, committing itself to the removal of all nuclear weapons from the United Kingdom and, in 1986, to the removal of US nuclear bases. The Social Democratic Party, founded in 1981 by moderate former Labor ministers, had by 30 September 1982 obtained 30 seats in Parliament, 27 of whose occupants were breakaway Labor members. In the elections of 9 June 1983, the Ch2nservatives increased their parliamentary majority, winning 397 seats and about 42% of the vote. The Labor Party captured 209 seats and 28% of the vote, its poorest showing in more than five decades. The Alliance of Liberals and Social Democrats won 25% of the vote but only 23 seats (Liberals 17, Social Democrats6). Minor parties took 5% of the vote and 21 seats.
In the elections of 11 June 1987, the Conservatives won 376 seats and about 42% of the vote. The Labor Party won 229 seats and 31% of the vote. The Liberal-Social Democratic Alliance won nearly 23% of the vote but only 22 seats (Liberals 17, Social Democrats 5). Minor parties took about 4% of the vote and 23 seats: Ulster Unionist (Northern Ireland), 9; Democratic Unionist (Northern Ireland), 3; Scottish National Party, 3; Plaid Cymru (Welsh Nationalist), 3; Social Democratic and Labor Party (Northern Ireland), 3; Sinn Feìn (Northern Ireland), 1; and Popular Unionist (Northern Ireland), 1.
The general election of 9 April 1992 resulted in a continuation of Conservative government under John Major with 42% of the vote and 336 seats. Labor followed with 34% of the vote and 271 seats. The Liberal Democrats took almost 18% of the vote, which netted 20 seats. Minor parties received 3% of the vote and 17 seats.
The Labor Party, under the leadership of Tony Blair, won a landslide victory in the general election of 1 May 1997, restoring it to power for the first time in 18 years. Of 659 possible seats, the Labor Party won 418 (43.1%), gaining 146 seats; the Conservative Party won only 165 seats (30.6%), losing 178 seats. The Liberal Democrats won 46 seats (16.7%), a gain of 26 seats since 1992 and the most seats held by the party since the 1920s. Other parties received 9.6% of vote, with the following representation after the 1997 elections: Ulster Unionist, 10; Scottish National, 6; Plaid Cymru, 4; Social Democrat and Labor, 3; Democratic Unionist, 2; Sinn Feìn, 2; Independent, 2; and United Kingdom Unionist, 1.
The June 2001 election was called "the quiet landslide" following the major victory of the Labor Party in the 1997 election. Labor won 40.7% of the vote and secured 413 seats; the Conservative Party gained only one seat (166) and registered 31.7% of the vote. The Liberal Democrats gained six seats (52;18.3% of the vote) from their historic high in 1997. Other parties received 9.3% of the vote, with the following representation after the 2001 election: Ulster Unionist, 6; Scottish National, 5; Democratic Unionist, 5; Plaid Cymru, 4; Sinn Feìn, 4; Social Democrat and Labor, 3; and Independent, 1.