Gordon Brown has asked the Queen to dissolve Parliament
Electioneering has begun in England after the prime minister announced the UK will go the polls on 6 May.
Gordon Brown spent 20 minutes with the Queen at Buckingham Palace to ask for the dissolution of Parliament.
Party leaders are heading to marginal seats across the country to begin campaigning in earnest.
Labour are behind in the polls but the Conservatives need the biggest swing since World War II to secure an overall majority.
Mr Brown, standing outside 10 Downing Street, pledged to renew public trust in politicians, saying politics had been "scarred" by recent events.
He said the Labour party would fight for fairness and declared: "Let's go to it".
Tory leader David Cameron said it would be the most important general election for a generation and that a vote for the Conservatives was a vote for a "fresh start".
David Cameron said he was "delighted" the campaign had begun
Liberal Democrat leader Nick Clegg said the formal announcement of a poll on 6 May spelled "the beginning of the end" for Mr Brown and insisted the campaign was "not a two horse race".
Parliament will be officially dissolved on 12 April.
Prospective MPs will be fighting for a total of 533 seats in England.
Boundary changes mean the new House of Commons will comprise 650 seats rather than the 646 contested in 2005.
A party requires 326 seats for an overall majority.
If Labour lose 24 seats it will lose its overall majority while the Conservatives need to gain 116 seats in order to secure an outright majority.
Campaigning in England is likely to focus on marginal seats, with the three in Ealing Central and Acton, Filton and Bradley Stoke, and Watford among the most crucial.
In each of these seats there is 10% or less separating the three main parties.
The scandal surrounding MPs' expenses has also seen a rise in the number of high-profile candidates squaring up against the established political parties.
Veteran TV presenter Esther Rantzen is standing in Luton South on an "anti-sleaze" ticket.
Nick Clegg said the election is "not a two horse race"
The MP who held the seat, Labour's Margaret Moran, is one of 144 MPs who have announced they will be standing down at the election.
Multi-millionaire Stuart Wheeler, a former Conservative party donor, has announced he is forming a new Trust Party to "clean up" Westminster in the wake of the expenses scandal.
Mr Wheeler will stand in Bexhill and Battle in Sussex, and has said he hopes to field at least two candidates elsewhere.
Key battlegrounds across England include the West Midlands, where Labour will be hoping to retain its appeal to middle-class voters in county towns like Hereford, Warwick, and Stafford - areas in which the Conservatives are hoping to recover lost ground.
In the north east Labour will be keen to hold on to as many seats as possible in a traditional heartland, but the Tories will also be eager to prove they can win seats in the region.
The south east, a Liberal Democrat stronghold, will be key to the fortunes of Nick Clegg's party. It will be keen hold on to voters that abandoned the Conservative party in previous elections to vote Lib Dem.
Meanwhile smaller parties including the Green Party, the BNP and UKIP are hoping this election will present them with an opportunity to win their first seats in the House of Commons.