How Britain's electoral system works

• Britain's Prime Minister can announce a general election at any time during their term of office, after first asking the monarch to dissolve Parliament.

• The country does not have fixed-term parliaments but elections must be held at least every five years.

• Britain operates a first-past-the-post voting system for general elections in which England, Wales, Scotland and Northern Ireland are divided up into 650 constituencies.

• Parliamentary constituencies historically each comprise roughly 70,000 voters but the boundaries are only redrawn every decade or so, and currently vary in size from 22,000-110,000 voters. Each elects one MP (member of Parliament) who sits in the House of Commons.

• Every person in that constituency can cast one vote for who they want to be their MP. Voters do not directly elect the prime minister.

• Assuming a party secures an overall majority - at least 326 members - in the House of Commons, its leader is asked by Queen Elizabeth II to form a government and also becomes Prime Minister.

• If no party has an overall majority in the House of Commons, there will be a hung Parliament - an extremely rare event in Britain that has not happened since 1974. But polls suggest this could be happen in the 2010 vote.

• This could lead to a minority or coalition government.

• However, the precedents for this lasting long-term are not promising - in 1974, two elections were held within nine months to resolve the situation.

• As well as being leaders of their parties, Labour Prime Minister Gordon Brown and Conservative leader David Cameron are also constituency MPs.