Hundreds of thousands of basic rate taxpayers will fall into the 40% income tax bracket when the government lowers the threshold next year.
The Budget small print shows the higher rate threshold will be reduced by £1,025, from £42,475 to £41,450, from April next year, capturing, experts suggest, as many as 300,000 extra people.
Osborne has been keen to stress a number of measures in today's Budget target the rich, after announcing the 50p top rate of tax would be cut to 45p from April next year.
From April 2013, the personal allowance will increase by £1,100 in cash terms to £9,205 - a measure worth about £170 a year after inflation to the typical taxpayer, he said.
But, at the same time, Osborne will lower the basic rate threshold by more than £2,000, from £34,370 to £32,245, meaning higher rate taxpayers will not get the full £170 saving.
Instead, the maximum they can get is one quarter of the benefit, or £42.50.
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