Gordon Brown was today likened to a used car salesman who had delivered a "dodgy" and "damaging" deal on Northern Rock.
And David Cameron criticised the prime minister for repeatedly refusing to confirm the extent of taxpayers' exposure over Northern Rock.
Mr Cameron said: "He is like a used car salesman: won't tell you the price, won't tell you the mileage. He's gone from Prudence to Del Boy without even touching the ground."
The Conservatives estimate £55 billion of public money has been poured into the troubled lender, including the reported £25 billion loan from the Bank of England.
'All of our customers are international and we need those transport links to be as efficient and effective as possible'
Mr Brown insisted taxpayers' money is secured against the bank's assets, with Northern Rock noted for its high-quality loan book.
But the Tory leader told the Commons the prime minister had delivered a "subprime deal for a subprime minister".
He said the rescue package was as much for Mr Brown's reputation as Northern Rock.
Ministers plan to turn the Bank of England's loan into government-guaranteed bonds, to be sold to private investors.
Liberal Democrat economic affairs spokesman Vince Cable criticised this plan, saying the government was nationalising the risks of Northern Rock but privatising the profits.
Today during prime minister's questions, Mr Brown said he was committed to getting the taxpayer the best deal from Northern Rock.
He defended the government's response to the bank's crisis, reminding the opposition benches they had supported the Treasury in September.
He said the Tories' attacks were the "height of opportunism" and accused Mr Cameron of "flip-flopping between nationalisation, privatisation and administration".
Mr Cameron quipped that the prime minister did not appear to know the difference between administration and liquidation: "Administration is what his government is in at the moment, liquidation is what it will be at the next election."
Former Tory chancellor Kenneth Clarke repeated the party line that Mr Brown had "dithered and delayed" on Northern Rock.
Lib Dem leader Nick Clegg said Mr Brown was refusing to nationalise Northern Rock because he was "running scared" of the Tories.
Mr Brown insisted all options were on the table, but a private-sector solution remained preferable.