The reason the OBR now famously forecast that public spending would fall to its lowest level since the 1930s under George Osborne's plans is his intention to continue cutting even once the deficit has been eliminated. Owing to £14.5bn of additional tightening in 2019-20, the Chancellor is predicted to achieve a surplus of £23bn, far beyond what most economists consider necessary to stabilise the public finances (a surplus of £4.8bn is forecast in 2018-19). It is this that has allowed Labour to accuse the Tories (as Ed Miliband did at today's PMQs) of having a plan for "shrinking the state", rather than merely "balancing the books". The party believes that the fear of slashed and burned public services could win it the election.

In an attempt to repair some of the political damage inflicted on the Tories, the Financial Secretary to the Treasury, David Gauke, told The Sunday Politics on 7 December that the party was not bound to a surplus of £23bn. He said: "We’ve made very clear we are committed to a surplus. At the moment the OBR predicts that we will have a surplus of £23bn, but we’re not making a commitment to the British people, 'that’s what the number will be in 2019'."

Appearing before the Treasury select committee this afternoon, Osborne had the chance to do the same and dispel the image of him as an unrelenting axeman. But when questioned on the subject, he instead argued it was necessary to continue cutting in order to reduce the national debt as a share of GDP. He also said: "It’s absolutely the spending proposals that I submitted to the OBR."

By emphasising the Tories' fiscal conservatism, Osborne is gambling that the voters will side with them over an opposition still viewed as profligate. But the opening he has provided for Labour means that fear of future cuts will now compete with fear of higher borrowing in the minds of voters. It is a battle that he is far from certain to win. As I noted yesterday, the latest ComRes/Independent survey found that 66 per cent do not believe that cuts should continue until the overall deficit has been eliminated with just 30 per cent in favour.

Labour's shadow chief secretary to the Treasury, Chris Leslie, has said in response: "George Osborne has finally admitted he approved the plans for deeper cuts which the OBR says will take public spending as a share of GDP back to 1930s levels.

"After two weeks when the Tories have tried to say it's somehow the BBC's fault, George Osborne has come clean that these are his plans. The Tories are now pursuing increasingly extreme and ideological plans for much deeper spending cuts which go well beyond balancing the books.

"In contrast Labour will take a tough but balanced approach to cut the deficit each year and balance the books as soon as possible in the next Parliament. Our plan will make sensible spending cuts in non-protected areas, fairer choices like reversing the Tory tax cut for millionaires and change our economy so we earn our way to rising living standards for all."