An incoming government will not only need to cut spending much more sharply than currently planned but will almost certainly also have to raise additional taxes, according to an analysis by PwC, the professional services group.

John Hawksworth, PwC's head of macroeconomics, was less optimistic than the government about the speed of a likely recovery from the recession and believed the next administration should aim to balance the budget by 2015-16 - two years earlier than Gordon Brown, prime minister, is proposing. That meant finding an additional £26bn of spending cuts or tax rises by 2013-14, when the next spending review ended.

The move was needed to reduce the risk that international investors would want higher interest rates on the UK's growing levels of public debt - and to build a buffer against a future recession, he said.

"We have been able to survive this major economic shock by throwing money at it," Mr Hawksworth said. "But who is to say in 10 years it won't happen again? So we should be planning to get back into surplus so that we have some money to throw at it, rather than ratcheting up the total of debt each time."

From 2020, the UK would also face higher costs from an ageing population: "You want to be in a strong position then to start meeting the pay-as-you-go benefits that will have to be paid".

The extra £26bn of fiscal tightening by 2013-14 could be met by tax rises or spending cuts. Taking it all from tax could damage growth. But taking it all from spending would produce "draconian" cuts - a 23 per cent reduction over three years in departmental spending if the health budget was protected.

A mix of tax rises and spending cuts "may be the most realistic" option, he said. A 50/50 split between tax and spending would still require cumulative cuts of 13 per cent in spending, or 18 per cent if health was protected - larger than the 9 per cent and 13 per cent likely on the government's current plans. But it would also require "significant rises" in the tax take of around £13bn, with income tax, national insurance or VAT likely targets.