Candidates aim to win a particular geographic constituency in the UK, and almost all are members of a political party. There are 659 constituencies, and thus 659 MPs. Most voters choose who to vote for based on the candidates' parties, rather than the personalities or opinions of the candidates.

Timing

A general election must take place before each parliamentary term begins. Since the maximum term of a parliament is five years, the interval between successive general elections can exceed that period by no more than the combined length of the election campaign and time for the new parliament to assemble (typically five to eight weeks).

The actual election may be held at any time before the end of the five-year term. The five years runs from the first meeting of Parliament following the election. The timing of an election is at the discretion of the incumbent Prime Minister. This timing is usually political, and thus if a government is popular the election is often "called" after around four years in power.

The Prime Minister asks the Monarch to dissolve Parliament by Royal Proclamation. The Proclamation also orders the issue of the formal Writs of Election which require an election to be held. The election is held 17 working days after the date of the Proclamation (per Representation of the People Act 1983, s 23 and Schedule 1 (Parliamentary election rules), rule 1 (Timetable)).

Since 1935 every general election has been held on a Thursday. Of the 16 general elections between 1945 and 2001, four have been in October, four in June, three in May and two in February.

The UK's Cabinet Office imposes Purdah before elections. This is a period of roughly six weeks in which Government Departments are not allowed to communicate with members of the public about any new or controversial Government initiatives (such as modernisation initiatives, administrative and legislative changes).