A source close to the Lib Dem president says he will vote against the government after party members "expressed their will very strongly against the Bedroom Tax".
The punitive penalty presents appalling dilemmas for vulnerable families. Ministers should finally accept that they have lost the argument.
The rebel Lib Dem says the policy is "Dickensian in its social divisiveness" and "victimises the most marginalised".
If the doctrine of ministerial responsibility means anything, the Work and Pensions Secretary should have resigned over the failure of Universal Credit long ago.
Outrage on Twitter directed at poster in the lobby of a Jobcentre in Manchester, but the policy isn't exactly new.
The new welfare system has been launched in just one new area, Hammersmith, rather than six as planned.
The cap is less a serious act of policy than a political weapon designed to trap Labour on the wrong side of the argument and to demonise the unemployed.
The new inflation figures show that it is under-indexation that will drive up child poverty rates inexorably.
In its determination not to refer to the "bedroom tax", the party mistakenly claims that Labour is "opposed" to the "spare room subsidy".
Rather than trying to outflank the Tories, the party needs to think harder about how to create a greater sense of collective identity and solidarity.