Leading economists have accused David Cameron of planning secret tax rises after the Prime Minister claimed Labour would pick voters' pockets.
The accusations intensified the row about the parties' plans, following claims the public is being kept in the dark until after the election.
The row came as new figures showed the UK economy grew faster than expected giving a pre-election boost to the coalition parties.
Mr Cameron attempted to capitalise on the good economic news by pledging an extra two million jobs over the next five years, delivering "full employment".
But union leaders described the promise as "ludicrous" and said the high number of posts created since the Tories came to power in 2010 was as a result of being elected during a recession.
But the biggest blow for Mr Cameron came from Paul Johnson, the director of the highly-respected Institute for Fiscal Studies (IFS).
He described a Tory claim to be able to raise £5 billion from tackling tax avoidance as "very flaky".
He added: "Where do you get £5bn from tax avoidance? We don't know. Given the scale of spending cuts they'll otherwise require they must be at least thinking about tax rises."
His comments came just 24 hours after the IFS said that Tories claims that Labour tax plans would cost £3,000 per household were unfounded.
Earlier David Cameron had ramped up his attack on Labour leader Ed Miliband.
He said that part of the choice in May's election was "about whether you want a government that will find savings and not pick into your pocket or, with Labour, a government that will pick your pocket, I think, on a pretty frequent basis."
Mr Cameron has been criticised for his partisan attack on Mr Miliband as he launched the election campaign outside Number 10.
The Tory leader said he made "no apology about putting the danger of Labour putting up your taxes squarely into this ...campaign."
There were problems for Labour also after a shadow minister appeared to raise the possibility that the party would balance the books three years later than planned.
Labour have said that they want a balanced Budget by 2020.
But Shabana Mahmood, the shadow exchequer secretary, appeared to raise the prospect that that date could slip to 2023.
Mr Cameron is also under increasing pressure over the Tories refusal to set out details on its plans for £12bn worth of welfare cuts after the election.
The Liberal Democrats urged the PM to "come clean", after he repeatedly ducked calls to spell them out.
Lib Dem spokesman Lord Scriven said: "David Cameron either doesn't know where the axe will fall, or he is not being honest with the public. Either way he is riding roughshod over some of the poorest people in society.
"The Conservatives might not think it's 'relevant' to say whether they would tax disability benefits or restrict child benefit to the first two children, but the people who rely on this support do."
The SNP said that their MPs would oppose austerity, including George Osborne's plans for another £30bn in public spending cuts.
The GDP figures showed that the UK economy was growing faster than expected, 2.8 per cent in 2014 - up 0.2 per cent from earlier estimates.
The Tories claimed the result showed that their "long-term economic plan" was working.
Liberal Democrat Treasury minister Danny Alexander said his party had been "the rock of stability on which this recovery has taken root".
Labour hit back saying at Tory attacks saying that all of its manifesto pledges would be fully costed, and accusing the Conservatives of planning "even deeper cuts in the next three years than we have had in the last five".
The party set out its own plan to cut and then freeze business rates, to help 1.5 million small businesses, funded by reversing a coalition cut in the main rate of corporation tax from 21p to 20p due to come into effect on April 1.
Mr Cameron said Labour's plan to hike corporation tax was "crazy" and Tories predicted it could cost almost 100,000 jobs.
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