By Nick Assinder
Political Correspondent, BBC News website
After months of speculation and a 24 hour postponement, Tony Blair is naming 5 May as general election day.
And, unlike the 2001 campaign, this one will prove historic, whatever the outcome.
Blair has delayed election announcement
Either Tony Blair will win an unprecedented third term, Michael Howard will pull off a sensational Tory revival or Charles Kennedy's Liberal Democrats will score the long-dreamed of breakthrough.
Campaigning will not reach full tilt until next week, following the Pope's funeral and the royal wedding and blessing, both of which the prime minister will attend.
It is also likely that the electioneering expected during the last session of prime minister's questions on Wednesday will be kept to a minimum, or abandoned altogether.
And, once the formal announcement is made, the government has only a few days to get as much of its existing business as possible through parliament, with some of it, including the ID card proposals, certain to be abandoned.
Latest polls suggest that the result may well be closer than previously believed. But the good news for the prime minister is that, even with his lead slashed to just 3%, he would still have a 100 seat Commons majority.
However, this is going to be a hard fought campaign and it started with some bad news for Mr Blair with one candidate jumping ship for the Lib Dems, while accusing the prime minister of authoritarianism, and the row over local Labour fraud surrounding the postal voting experiment.
Howard will delay campaigning
The prime minister has insisted it will be fought on the economy and a stark choice between, he claims, Labour's stability and investment against Tory cuts and boom and bust.
He is likely to urge voters not to use it as a referendum on the government's past performance, but as a time to make that crucial choice.
Tory leader Michel Howard is also likely to concentrate on the economy with claims another Labour government would be forced to raise taxes again.
And the Liberal Democrats' Charles Kennedy will focus on his "fair tax" proposals to raise taxes for earnings over £100,000 to pay for investment in public services.
During the phoney campaign, Labour got into trouble over its central claim that Michael Howard was planning £35 bn cuts in public services.
The prime minister found himself struggling to explain how a smaller, slower increase in spending planned by the Tories compared to Labour's plans was a cut.
And it looked like the Labour campaign - which was already being criticised for being thrown into defensive mode by Mr Howard on issues such as immigration and health - was on the rocks.
Then deputy Conservative Chairman Howard Flight was reported to have suggested Mr Howard was secretly planning even bigger "cuts".
He was sacked for his gaffe, but the damage had been done and the faltering Labour campaign was back on track.
The Tories have since attempted to get back to their central message that Chancellor Gordon Brown has to fill a black hole at the centre of his finances and will be forced to raise taxes if Labour wins again.
As usual, the Liberal Democrats will have to fight to get their voice heard over the sounds of battle between the two big parties.
Kennedy is on election standby
But leader Charles Kennedy believes he has set out a distinctive manifesto with plans for a tax rise for the wealthiest to finance extra spending and the abolition of the council tax in favour of a local income tax.
Other issues are certain to play a part - immigration and asylum, the war on Iraq, law and order, health and education, for example.
Whatever that outcome, 2005 is set to be an historic poll - either handing Labour an unprecedented third term, the Conservatives a sensational victory or the Liberal Democrats the breakthrough they've wanted for so long.