4.45pm update
As the prime minister and chancellor campaigned together again today, this time in Edinburgh, Labour published an overnight 30-page "demolition job" of Tory figures, claiming that the party was counting savings "from day one" which would take at least two years to kick in, after a Tory election victory.
Labour's own manifesto is published tomorrow, and the Tories say there will be an £11bn tax shortfall "black hole" under a third Labour term.
Tonight Labour's Alistair Darling lead the attack, saying: "A gaffe-prone Conservative party has failed to clear up the confusion about its tax policy.
"This lunchtime, Oliver Letwin suggested that the Tories' tax cuts wouldn't come in until 2007/08, but this morning, shadow chief secretary [to the Treasury] George Osborne said that their tax cuts would come in 2006/07.
"And yesterday, David Cameron said that the Conservative party's tax cuts would happen right away - 2005/06.
George Osborne, a Tory Treasury spokesman, told Sky today that "the spending savings ... begin on day one", before admitting that they would "take two years to implement", and clarifying that the "programme begins on day one".
At this morning's Labour press conference, Mr Brown said an analysis of the Conservatives' manifesto showed they were offering the "extraordinary combination of a black hole and severe public spending cuts".
And he warned that if the deficit was met by increased public borrowing, the Bank of England might be forced to increase interest rates.
The Liberal Democrats joined in the attack on Tory spending plans. The party's Treasury spokesman David Laws described £8bn of the their projected savings as "unrealistic".
Mr Blair, meanwhile, warned: "These proposals are a complete economic mess and that will be an economic risk."
The joint performance from Mr Blair and Mr Brown - after five days which has seen the pair constantly together - lasted more than an hour. The Tories were not holding a press conference of their own today, but the shadow chancellor defended his plans on Radio 4 and accused the government of planning tax increases. The Tory party chairman, Liam Fox, later attempted to rebut Labour's "demolition job".
He said: "While it is flattering for Labour to spend so much time trying to find a chink in the Conservative economic case, it is astonishing that, after eight years in power, they can think of no better reason for being re-elected than that they are not us."
This morning the shadow chancellor, Oliver Letwin, insisted that the independent Institute of Financial Studies was confident of the Tories' ability to find £4bn worth of tax cuts.
At Labour's press conference, Mr Brown was pressed by reporters to rule out any tax rises in a Labour third term. He merely said: "No politician has been well served by making absolutist commitments like that", and pointed to John Major's experience of promising increased spending, lower borrowing and tax cuts before the 1992 election.
Mr Blair said the relative situation of the Labour and Conservative parties had been reversed from the time in the 1980s when Labour was accused of uncosted spending promises.
He added: "The Tories' problem is that they have an unresolved contradiction between those who want to lower public spending and [those] who accept spending increases. That's why they have ended up with this mess.
"It's a flimsy manifesto because they haven't decided what they want to be."
Mr Blair said the Tories had "no idea" how they would find their promised £869m savings in the immigration service, while looking for an "offshore processing centre" for asylum seekers and also promising a 24-hour border patrol service.
Alistair Darling raised laughter by saying that the Tories had promised to find £100m of savings through outsourcing the driving tests assessment centre - something the Tories themselves had already done in 1996.
Mr Brown attacked the Tory manifesto - 28 pages long - as a document of "few words, and fewer figures".
He said it was "a shopping list of promises that do not and cannot add up". It would, he said, repeat the mistakes of John Major's 1992 government which he said ran up "the biggest deficit in our history".
The Conservative Party manifesto, launched earlier today, has been criticised by opponents as being unrealistic.

The pledge of £35 billion of savings from "government slimlining", and subsequent tax cuts, has been attacked by Labour and the Liberal Democrats.  The Conservatives plan to continue funding front-line services at the current rate by relying on economic growth to make up the difference.  

Labour described the plans as "a complete economic mess", the current Chancellor, Gordon Brown claiming there would be a shortfall of "£18.9bn in year one, £18.5bn in year two and £14.4bn in year three."  Labour leader Tony Blair claimed that the Labour and the Conservatives economic roles had reversed since the 1980s, when many had lost faith in Labour's ability to handle the economy.

The deputy leader of the Liberal Democrats, Sir Menzies Campbell, claimed that £5.5 to 8 billion of cuts were unrealistic.

Labour's manifesto is launched tomorrow, and the Liberal Democrats launch theirs on Thursday.  Conservative shadow Chancellor Oliver Letwin has already criticised Gordon Brown's budget of March this year, claiming it will create an £11bn shortfall.