Chancellor George Osborne and Work and Pensions Secretary Iain Duncan Smith dismissed criticism that they said made the shake-up sound like “the beginning of the end of the world”.
They launched a fightback as 660,000 social housing tenants with a spare room began to lose an average £14 a week in what critics have dubbed a bedroom tax.
It is part of a package of welfare and tax changes coming into force this month which critics claim will hit poor families and the disabled especially hard.
Changes to council tax benefit will see bills for an estimated 2.4 million households rise an average £138 a year with two million paying for the first time, an anti-poverty group said.
The system has been handed to town halls to operate from today.