Why is the Coalition expected to borrow more than the Office for Budget Responsibility forecast in June 2010? Labour would argue it is because George Osborne's austerity drive knocked the stuffing out of the economy. All that talk of deep cuts prompted fearful households and businesses to stop spending and has undermined tax revenues. George Osborne would, however, pin the blame on the confidence-draining eurozone crisis. He would also argue that Labour's less ambitious deficit reduction plan would have resulted in a run on British government debt, putting us in the same boat as Greece and Italy.

So who is right? Many will find Labour's argument more compelling given that the British economy was showing alarming signs of weakness long before the eurozone crisis reached boiling point this year. But the only way to prove this beyond doubt would be to go back in time, implement Labour's March budget and watch what happens to borrowing levels. Without that, Mr Osborne will be able to argue that it would have been still worse under Labour.