PM to announce 6 May general election
The three main party leaders will go head-to-head live on television
Gordon Brown will announce on Tuesday morning that the general election will, as expected, be held on 6 May, BBC political editor Nick Robinson says.
The prime minister will go to Buckingham Palace to ask the Queen to dissolve Parliament.
On returning from the Palace he will formally confirm the date and make a speech in Downing Street in which he will dub the election "the big choice".
The economy, taxation and public services will be key battlegrounds.
The campaign will also feature, for the first time, live television debates between the three main party leaders.
It will be the first time that Mr Brown, David Cameron and Nick Clegg have led their respective parties into a general election.
We are in for most unpredictable, most dramatic and most exciting election in many years - I can't wait
Nick Robinson
Nick Robinson's blog
On returning from the Palace, Mr Brown is expected to say: "The people have fought too hard to get Britain on the road to recovery to allow anybody to take us back to the road to recession."
He will outline "three big challenges" facing the country - securing the recovery, protecting front-line services whilst halving the deficit, and renewing politics.
At about the same time, Mr Cameron will make a speech in which he is expected to say the Tories are fighting for "the Great Ignored".
"We're fighting this election for the Great Ignored - young, old, rich, poor, black, white, gay, straight.
"They start businesses, operate factories, teach our children, clean the streets, grow our food and keep us healthy - keep us safe. They work hard, pay their taxes, obey the law," he will say.