Cameron said: "The prime minister is like a second hand car dealer. He won't tell you the price, he won't tell you the mileage and he will not give you a warranty.”
The Prime Minister responded with the accusation that the Tory leader was "all slogans and no substance".
The heated exchanges came after the Government announced plans to turn Northern Rock's £25 billion loan from the Bank of England into bonds to sell to investors. The bonds would be guaranteed by the Government to speed up a private sale. If a private sale is not reached, the bank will come under temporary public ownership.
But Cameron said taxpayers had a right to know what their total exposure was under the Government's plans for the troubled bank - before adding that he believed it was £55bn.