Gordon Brown and David Cameron have clashed again over public spending plans at Prime Ministers' Questions.
Mr Cameron mocked Mr Brown for forecasting a "0% rise" in 2013/14.
But Mr Brown said Mr Cameron's spending plans were based on a rise in unemployment "because you will do absolutely nothing about it".
Earlier, Lord Mandelson accused George Osborne of a "deliberate untruth" after the shadow chancellor said he was denied access to data.
Both Labour and the Conservatives are under pressure to spell out what spending cuts will be needed to rebalance the public finances and reduce public debt.
In the Commons, Mr Cameron accused ministers of avoiding a spending review "because they do not want to own up to the cuts they are planning".
But Mr Brown replied that it would be "completely wrong to have a spending review now at this stage because we are in the midst of a recession", and future performance was impossible to predict in such circumstances.
He said the Tories had made their estimates about the necessary level of cuts in public spending because "they assume unemployment will rise - that's not the policy of this government".
George Osborne: "He (Brown) has denied us access to that information"
Mr Cameron said it was Labour which was responsible for rising joblessness.
"There's only one person we want to put on the unemployment register and that's the prime minister," Mr Cameron added.
Later the prime minister's spokesman said when Mr Brown predicted a "0% rise" he meant to say "0.7% rise" in current spending but had then been interrupted.
Lib Dem leader Nick Clegg said the "bogus debate" on public spending between the two largest parties had hit "new lows", and accused both Mr Brown and Mr Cameron of avoiding the truth.
He accused Mr Brown of "living in complete denial" about long-term savings which will be needed to balance the nation's books and claimed Mr Cameron wants to cut spending now which would be "economic madness".
The row came after Business Secretary Lord Mandelson accused Mr Osborne of staging a "smear" by claiming he had been denied access to government data.
On Tuesday Mr Osborne said the prime minister had intervened to stop him seeing a database which would help him decide how to reduce public spending.
Mr Osborne pledged to publish the data so the public could "know the truth".
There is, of course, an underlying tale here which has nothing whatsoever to do with public spending
But in a statement, Lord Mandelson said the "very serious allegation" had been rejected by Cabinet Secretary Sir Gus O'Donnell.
"There is a very unattractive pattern of behaviour that is starting to emerge with George Osborne, of innuendo in pursuit of a smear," Lord Mandelson said.
Lord Mandelson told the BBC News Channel: "Mr Osborne had said something about the prime minister which he knows to be untrue.
"He should step back, consider what he said and withdraw something that is untrue."
Mr Osborne said on Tuesday ministers had turned down a request for the opposition to look at a database - known as the Combined Online Information System - which lists government spending in 12,000 categories.
"Gordon Brown is denying to the opposition the information on spending items in the government budget which would help us plan for government, help us plan for dealing with the debt crisis," he said.
"That makes our life as an opposition more difficult but, more to the point for the country, it means the country doesn't know the truth about where their money is going."
A Downing Street spokesman said the request was a matter for senior civil servants and it would be "completely inappropriate" for the prime minister to become involved.
He said there were normal conventions surrounding information made available to the opposition and the prime minister believed these should be followed.
Mr Osborne also told the BBC the Conservatives would not ring-fence schools spending.
In an interview with the BBC's Political Editor Nick Robinson, he said that only spending on health and international development would be explicitly protected by a future Tory government.
Ministers insist that real spending can increase after 2011 if tough decisions are taken on tax and "efficiencies" and accuse the Tories of planning 10% cuts in many areas.
But the Tories say Labour is trying to close down the debate on spending and will not admit cuts will be needed whoever wins the next election.
Mr Cameron warned earlier this week that "riots on the streets" would be risked if parties went into an election without making clear that spending cuts would be necessary afterwards.
He also said that he thought there was a "thread of dishonesty" running through Gordon Brown's prime ministership.
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