Government support for the bedroom tax looked as if it was on the verge of falling apart today, after Liberal Democrat president Tim Farron broke ranks on the policy.
The intervention comes after a report by an influential committee of MPs corroborated many of the concerns about the policy's effect on disabled people.
"The onslaught of divisive rhetoric that demonises the poor can never help us to create a fairer society," Farron will tell the Centre for Social Justice later.
"The bedroom tax causes huge social problems and distorts the market – we as a party cannot support this."
Farron's attack on the bedroom tax does not constitute a change in Lib Dem policy, although it comes after the party conference agreed to review it and comes hot on the heels of pledges from Nick Clegg to give local councils more flexibility in providing discretionary support to hardship cases.
Labour was unimpressed by Farron's conversion.
"This is breathtaking hypocrisy from the Lib Dems," a spokesperson said.
"The bedroom tax is their tax, just as much as it is David Cameron and the Tories' tax. Their support made it happen and no amount of weasel words will change that."
A report by the work and pensions committee today found there had been financial hardship for vulnerable people as a result of the policy, which cuts housing benefit according to how many spare bedrooms people have.
The coalition was warned that the policy would penalise disabled people who usse the spare bedroom to store medical equipment or accomodate a carer.
Cameron often responds to criticism of the policy by stressing that discretionary housing payments are available to people in hardship, but the committee found this was a temporary measure whichincluded different elibility rules in different parts of the country.
"Vulnerable groups, who were not the intended targets of the reforms and are not able to respond by moving house or finding a job, are suffering," committee chair Anne Begg said.
"The government's reforms are causing severe financial hardship and distress to vulnerable groups, including disabled people.
"Sixty to seventy per cent of households in England affected by the [bedroom tax] contain somebody with a disability and many of these people will not be able to move home easily due to their disability.
"So they have to remain in their homes with no option but to have their housing benefit reduced."
The committee recommended that anybody living in a home which has been significantly adapted for them should be exempt from the bedroom tax and that all households that contain a person in receipt of higher level disability benefits should also be excluded.