Did you know?
The most votes: The Conservative party in 1992 won the most support in any general election with 14,094,116 votes.
Largest and smallest majorities: The largest majority of the 20th century was for the National government of 1931, which had 491 more seats than its opponents. The smallest was Labour's lead in 1964 - just four seats.
Most campaigns: Tony Benn, MP for Chesterfield, holds this record. He has been involved in 17 elections.
Image: The British appear to prefer clean-shaven leaders. The last prime minister to have a beard was Lord Salisbury who held office in 1885-86 and 1895-1901.
Who can vote?: You cannot vote if you are under 18, or a convicted criminal who has been jailed for more than a year.
You can vote if you are a hereditary peer not sitting in the House of Lords, but you can't if you have been convicted over the past five years of corrupt or illegal practices during an election, are serving a prison sentence of more than 12 months or being detained under the mental halth act. Oh, and you must be registered to vote. The Queen can but doesn't.
Oldest and youngest: William Pitt the Younger (pictured right) became the youngest prime minister at the age of 24. Sir Francis Knolly was 90 when he was re-elected MPfor the last time, while in 1435 Henry Long became one at 15.
Voting: Before 1918 only certain people could vote. It depended on their age, wealth and class. After World War 1, Acts were passed by Parliament to allow more people to vote. In 1918 the right to vote was extended to all men aged 21 and over and women of 30 and over. In 1928 the voting age for women was lowered to 21. The current voting age for men and women - 18 - was introduced in 1969.
PM's title: The official title for the first minister used to be First Lord of the Treasury. "Prime minister" was initially a derisory term but became commonly used in the 19th century. Benjamin Disraeli liked the term and allowed people to use it when he was prime minister in 1868 and 1874-80.
When do we vote?: At least every five years. But a prime minister can, and often does, hold one at an earlier date.