Prime Minister Gordon Brown can call a General Election at any time up to May 2010. Once he calls it, what are the rules about the campaign timings?
ONCE AN ELECTION IS CALLED
General Election campaigns normally last between four and six weeks - but legally they can be as short as 17 working days.
The official countdown begins once Parliament is dissolved. There is normally a gap between the prime minister announcing his request for a dissolution and the issuing of a royal proclamation.
There is no fixed limit for this intervening period. In recent history it has been two or three working days to allow Parliament to conclude any outstanding business.
The exception was 1997 when John Major announced 1 May as polling day - 22 days before the statutory election timetable was triggered.
The following timetable shows what happens once Parliament has been dissolved.
A Royal Proclamation dissolves Parliament and also orders issues of writ for the election of a new Parliament - formally setting the date - which go out to returning officers.
Writs are received.
Deadline for notice of election to be published by returning officers is 4pm.
Nomination papers for / withdrawals of candidates must be delivered by 4pm. Election agents must also be nominated by 4pm. Nominations are announced by 5pm, once any objections are settled.
Deadline for receipt of absent voting applications - people who cannot reach a polling station and want to vote by proxy or by post - is 5pm.
The last day for polling and counting agents to be appointed.
Earliest possible election day (polls open between 7am and 10pm)