Jonathan Isaby from the TaxPayers' Alliance said taxpayers would "resent" paying for spare rooms for those receiving housing benefits "when they can't have one themselves."
He said: "I'm not saying that there aren't people who do need those rooms but you can't have a blanket exemption for hundreds and thousands of people."
Campaigners against the Government's so-called 'bedroom tax' will take to the streets tomorrow in protest of the proposals.
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Former Conservative party chairman says the mistakes of two Tory Prime Ministers in row have had "calamitous" consequences for Britain.
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The Brexit Secretary's comments come after Chancellor Philip Hammond's remarks that no EU deal would "very, very bad" for the UK.