Q+A: How do Britain's elections work?

LONDON (Reuters) - Britain votes on Thursday to elect a new parliament in an election that could redraw the political map. Below are answers to some key questions about British elections.

Q. What are people voting for?

A. In a general election, people in each voting area or constituency around Britain vote for one member of parliament (MP) to represent them in the House of Commons, the lower chamber.

The 2010 general election will use new constituency boundaries, meaning that afterwards there will be 650 seats in the Commons representing constituencies across England, Wales, Scotland and Northern Ireland. At present there are 646 seats.

However, the death of a candidate during the campaign means that the vote in the Thirsk and Malton constituency in northern England has been delayed until May 27.

Q. How is an MP elected?

A. Each eligible voter has one vote in their constituency, and the candidate with the most votes becomes the MP for that area. Candidates do not need an overall majority to win. This voting system is called "first past the post."

Q: Who forms the government?

A: The political party with the most MPs usually forms the government -- though two or more parties with a combined majority of MPs may form a coalition government.

Q. What is a hung parliament?

A. A hung parliament is one in which no party has more than half of MPs in the House of Commons, meaning that the largest party needs the support of others to pass legislation.

The opposition Conservatives are favorites to emerge as the largest party, according to most opinion polls. But to obtain an overall majority they would require a swing of 6.9 percent in the national vote from the ruling Labour Party. This would be a bigger swing than in any election since 1950, except 1997.

Q. How is the prime minister chosen?

A. The leader of the party with the largest number of seats in parliament usually becomes prime minister.

The incumbent, Gordon Brown, became prime minister in 2007 after his predecessor Tony Blair resigned in mid-term and Brown succeeded him as leader of the Labour Party. This is the first time Brown has led the party into a general election.

Q. How often are general elections held?

A: There has to be a general election at least every five years. The prime minister decides when to call an election. The current Labour government has been in power since May 5, 2005.

Q: Who can vote?

A: British citizens, plus Commonwealth and Irish citizens living in the UK, who are over 18 years old on polling day can vote, as long as they are on the electoral register.

Members of the House of Lords, which is the upper chamber of parliament, as well as convicted prisoners and anyone guilty in the previous five years of corrupt or illegal election practices, cannot vote.

Sources: www.parliament.uk, www.direct.gov.uk