Five years is the maximum period for a Parliament. This is specified within provisions contained under the Septennial Act 1715, amended by Section 7 of the Parliament Act 1911.
The five years run from the first meeting of Parliament following a UK Parliamentary general election. The current Parliament was first summoned on Wednesday 11 May 2005, so will cease to exist at midnight on Monday 10 May 2010. A general election to elect the new Parliament must be held by no later than Thursday 3 June 2010.
The House of Commons library has produced a research paper on Parliamentary election timetables (PDF), and the Electoral Commission produced a report Election timetables in the United Kingdom (PDF) in July 2003.
