But James Brown, senior research economist at the IFS, said: “Alistair Darling’s income tax increases for the rich will significantly complicate the tax system, and may well raise little revenue. A simpler and smaller increase in tax rates across a broader range of high-income taxpayers would raise the money the Treasury is looking for more efficiently, especially if combined with measures to make income tax harder to avoid.”

The IFS report said it was “extremely unlikely” the Treasury would raise £3.2 billion from the new tax rate and personal allowance reforms.

It said the Government would be more likely to raise £3 billion by creating a 60 per cent tax band for all those earning more than £100,000 a year.

It said it “may well be impossible” to raise extra revenues from the one per cent of the population on incomes above £150,000 by just increasing the tax rate above that level. But the IFS said the Government could raise the £3.2 billion by increasing the higher rate of income tax on earnings above £43,875 from 40 per cent to 43 per cent.