The House of Commons is the main lawmaking body for the United Kingdom, the other being the unelected House of Lords. It consists of 650 members, each of whom is elected by a geographical constituency of roughly equal population.
In each constituency, the candidate with the largest number of votes wins. There is no need to win 50% of the vote, and votes for other candidates are in effect lost. This is known as first-past-the-post voting.
The Commons also chooses the prime minister. By convention, the monarch invites the leader of the largest party to form a government. The prospective prime minister needs to have the support of the majority of MPs. This is possible if they lead a party with an overall majority or have the backing of other parties.
A majority technically requires 326 MPs (half of all seats plus one), but a small number of MPs – including the speaker, his deputies and the members of Sinn Féin – do not usually vote. This means a working majority can be achieved with just under 50% of seats.
