The national legislative body in Britain is made up of two parts: the lower chamber is the House of Commons, made up of 650 elected Members of Parliament; the upper chamber is the non-elected House of Lords.

The Prime Minister

Most successful candidates for the House of Commons are members of the Conservative Party or Labor Party. The leader of the majority party in the Commons is prime minister. He or she is not elected directly by the voters, but chosen by fellow party members.

Electing the Prime Minister

Each party has its own rules for electing a leader. The Conservative Party, which has a 98-seat majority in the Commons, will choose its new leader by a secret ballot on Tuesday. If no candidate wins a majority, there will be a final ballot on Thursday.

The Transition

Margaret Thatcher remains prime minister of the United Kingdom of Great Britain and Northern Ireland until the governing Conservative Party chooses a new leader next week. At that time, she will submit her resignation to Queen Elizabeth II. The party's new leader will meet the monarch soon afterward to be confirmed as prime minister, probably within an hour.

Terms of Office Parties are elected to govern for a maximum of five years, but a British prime minister can call a general election at any time. The present Conservative government's term runs out in mid-1992.

SOURCES: The Washington Post; Associated Press