But after Ed Miliband's response, the Prime Minister tried to counter-attack. He began by saying of the Labour leader's speech, "I don't know who writes this rubbish" which drew one of Ed Balls' infamous calm down gestures. Cameron then offered an aggressive defence of the IMF, calling it an "organisation that rescued us from Labour in the 1970s". He went on to accuse Miliband and Balls of "putting the politics ahead of the economics".
But the questions from Tory backbenchers exposed the serious reservations on the Prime Minister's own benches about Britain underwriting a larger IMF. The politics of this is going to be very tricky for the coalition.
One moment of light relief came when Cameron said that if the French are going to keep pushing for a financial transactions tax which would raise 80 per cent of its revenue from London-based firms, then he would propose a cheese tax. The line drew lusty cheers from the otherwise quiet Tory benches.