Government departments have amassed more than £20bn in underspends, the Treasury revealed on Thursday, adding to the problem of public expenditure control over the next decade.

The announcement of the totals built up under what is termed “end-year flexibility” – money which departments have a right to spend – came on the same day when the International Monetary Fund’s annual assessment of the economy confirmed its initial recommendation to bring forward more concrete and rapid plans to cut the £175bn deficit in the public finances this year.