Boris Johnson has pledged to cut income tax for three million higher earners, in a move that would cost £9.6bn a year.
The current frontrunner in the Tory leadership contest said he would raise the threshold for the 40p tax band from £50,000 to £80,000 if he becomes prime minister.
The move would be paid for through money currently set aside for no-deal Brexit planning and by rises in National Insurance.
Mr Johnson said: “We should be raising thresholds of income tax – so that we help the huge numbers that have been captured in the higher rate by fiscal drag.”
But the announcement sparked immediate criticism, including from senior Conservatives.
Nicky Morgan, the chair of the Commons Treasury committee, said: "The question for Boris is why is this a priority when you could be obviously lifting more people out of paying income tax - the lower rate taxpayers - or you could be give people receiving child benefit an extra £15 a week."
And Amber Rudd, the work and pensions secretary, said: "If you want to badge yourself as a One Nation Conservative, you focus on tax cuts and investment in infrastructure to help the lowest paid and the people in most difficulty in all parts of this country. That's not what he's doing."
Conservative MPs have until the end of Monday to formally enter the leadership contest, which is due to run for around a month.
Several of the candidates have already set out plans to cut taxes if they win the race to succeed Theresa May.
Jeremy Hunt, the foreign secretary, said he wanted to cut corporation tax from 19 per cent to 12.5 per cent, while Dominic Raab, the former Brexit secretary, promised to focus on low-earners, including cutting the lowest rate of income from 20p to 15p.
Sajid Javid, the home secretary, has suggested he could lower the threshold for the highest tax rate from the current £150,000.
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