Prime Minister Gordon Brown and Conservative leader David Cameron have clashed angrily over public spending.
At Prime Minister's Questions, Mr Cameron said Mr Brown should admit government plans would mean real-terms cuts after 2011, which Mr Brown denied.
Mr Brown said the Tories wanted to "spend less, 10% less in most departments - we want to spend more".
But Mr Cameron said Mr Brown was not being straight and was "simply not worthy to be our prime minister".
The Conservative leader said both capital and current spending were to be reduced, but the prime minister was trying to take the country for "fools" by claiming spending would continue to increase.
He added: "Whichever way you look at the figures, whichever way you look at the figures, the government plans to cut spending.
The only certainty is that this kind of crisis will happen all over again
Nick Clegg Lib Dem leader
"He wasn't straight over the cancelled election, he wasn't straight over the 10p tax, he wasn't straight on flying to Iraq in the Tory conference, he wasn't straight over Damian McBride, he wasn't straight on who he wanted as his chancellor, and now he won't be straight with people about the level of government spending."
But Mr Brown said there was "good evidence" that government measures were helping bring the UK out of recession and denied that spending would fall in real terms after 2011.
"We are spending money to take people out of recession," he told Mr Cameron.
"You would cut the money now - there would be more unemployment, more debt and more deficits."
Lib Dem leader Nick Clegg said the prime minister had failed take the opportunity to properly regulate the banks, saying he had let them get away with "blue murder".
Mr Clegg added: "Can't he see if he just keeps passing the buck, the only certainty is that this kind of crisis will happen all over again?"
But Mr Brown said the government was implementing better regulation, and the G20 summit in London had been about improving cross-border supervision.
The prime minister added: "To be honest, I think he actually supports what we're doing but can't bear to say it."
The row over spending came after Chancellor Alistair Darling warned that the country would have to "live within our means" and oversee a slowdown in public spending growth.
But he declined to endorse cabinet colleague Andy Burnham's claim that health spending would keep rising.
Mr Darling told the BBC's Today programme he had "quite deliberately" stated in his Budget he had not yet allocated post-2011 funding.
In Monday's Times, Shadow Chancellor George Osborne said all parties should admit there will be spending cuts.
Last week, Tory health spokesman Andrew Lansley appeared to suggest that, in order to protect spending on the NHS and schools, a future Conservative government would cut expenditure in other areas by a total of 10% between 2011 and 2015.
The Conservatives said he had been working from Labour's own figures from the last Budget but the prime minister accused the Tories of planning "savage" public spending cuts.
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