Labour is to stay with the pledges made at the 1997 and 2001 elections not to raise the basic and top rates of tax.

The FT reports that although the tax section had not yet been finalised by the prime minister and the chancellor, extending the tax pledge could be ruled out.

“The final decision depends on a meeting between the two principals, which is imminent,” said one Downing Street figure.

“But my bet is there will be no extension of the pledge, because you then go down the slippery slope of having to justify what you've ruled in and what you've ruled out.”

An ally of the chancellor added: “It would come close to repeating the disastrous commitment made by John Major in 1992 not to raise the tax burden, and neither Gordon Brown nor Tony Blair would do that.”

Meanwhile, Vincent Cable tells the FT that he is facing criticism from former City colleagues over the party's proposals to impose a 50 per cent top rate.

The Liberal Democrat Treasury spokesman said the political debate about tax was "misleading and dishonest" because people would pay more tax whether or not the next government changed rates or thresholds.