Prime Minister Gordon Brown on Tuesday called a general election for May 6.

Brown traveled to Buckingham Palace where he asked Queen Elizabeth II for permission to dissolve parliament -- a formality that marked the start of the official election campaign.

Flanked by the cabinet, Brown said the Queen has agreed to the dissolution of Parliament and the election will take place May 6.

Following are the basic facts of the general election posted on UK parliament's website:

When Parliament is dissolved，every seat in the House of Commons becomes vacant and a general election is held. Each constituency in Britain elects one MP (Member of Parliament) to a seat in the House of Commons. The political party that wins a majority of seats in the House of Commons usually forms the government.

How often are general elections held?

General elections are held at least every five years although not all Parliaments run for the whole five-year period.

How does it work?

MPs are elected from a choice of candidates by a simple majority system in which each person casts one vote. The candidate with the most votes then becomes the MP for that constituency.

Candidates may be from a political party registered with the Electoral Commission or they may stand as an "Independent" rather than represent a registered party.

Where do people vote?

Most voting takes place in polling stations but anyone eligible to vote can apply for a postal vote. British citizens living abroad are also entitled to a postal vote as long as they have been living abroad for less than 15 years.

Last general election

The last general election in Britain took place on May 5, 2005.