Gordon Brown will need to raise taxes by £5 billion a year if he is to extend current spending levels over the next three years and fulfil pledges to rebuild public services.

A study by the Institute of Fiscal Studies questions the chancellor's record, finding that public spending levels have been lower under Labour and the nation's tax bill higher.

The report also finds that despite Brown's budgets favouring the less well off, the gap between rich and poor has continued to grow. The IFS argues that Brown's "war chest" would comfortably cover current plans to boost services until 2003 - 2004 but planned increases of 3.8 per cent per year in following years would require a tax rise equivalent to 2p on the basic rate of income tax.

The influential think-tank has provoked the first serious political row of the election campaign with the Conservatives seizing on the figures and claiming a £5 billion "black hole" in Brown's finances.