Millions of middle and higher earners will be hundreds of pounds a year worse off because of surprise changes to tax and national insurance.

Anyone earning more than £40,000 will pay more from 2011 because of a 0.5 per cent increase to national insurance. Those earning £150,000 or more – about 350,000 people - also face a new top rate of income tax of 45 per cent. A year before that, those with incomes of £100,000 or more will see a cut in the value of their personal allowance – the amount they earn before tax.

The small print also revealed that tens of thousands more people could be dragged into the higher-rate tax band from 2011. That is when the Chancellor plans to freeze the higher-rate threshold above which people pay 40 per cent tax, a move that accountants described as a classic “stealth tax”. The threshold usually rises in line with inflation each year.

Richard Mannion, of the accountant Smith & Williamson, said: “This is a set of Robin Hood initiatives, with income tax rises aimed at the better-off to enable giveaways to low-earning families.” The new 45 per cent rate has been widely mooted. Someone earning £200,000 will pay an extra £2,500 a year, he said.

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The other measures came as a surprise, especially the changes to the personal allowance for high earners. From April 2010 the allowance will be reduced by £1 for every £2 by which income exceeds £100,000. Up to £140,000 it cannot be reduced by more than half, so if the personal allowance in 2010 is £6,475 it cannot drop below £3,240. For incomes above £140,000 the personal allowance is removed altogether.

Maurice Fitzpatrick, of the accountant Grant Thornton, said: “The proposal to withdraw the income tax personal allowance from people earning over £100,000 unleashes a barrage of somewhat arbitrary, and very high, marginal tax rates for higher earners. People earning £100,000, for example, will have a marginal income tax rate of 60 per cent.”

The measures combined mean that people earning £40,000 to £100,000 will, from 2011, be paying an average of £156 a year more in income tax and national insurance. Those earning £100,000 to £140,000 will pay £1,144 a year more, and with incomes of £140,000 to £200,000 will see their bill jump by an average £3,172 a year.

The news is better for many basic-rate taxpayers. In September Alistair Darling raised the annual personal allowance from £5,435 to £6,035 to repair damage caused by the withdrawal of the 10p tax band. The increase was introduced for the current tax year but the Chancellor announced yesterday that it will be permanent and he guaranteed an above-inflation increase in the allowance from April to £6,475.

Damage caused by the rise in national insurance in 2011 will be offset for lower earners by the starting point for national insurance being aligned with that of income tax.

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