The government has lost a record eighth vote in the House of Lords over its plans to severely cut and restructure the British welfare system.
An amendment to the Welfare Reform Bill, overturning a move to cut payments to specific council tenants with one spare bedroom, was carried by ten votes.
The bill is now due to go back before the House of Commons, with the government defiant but a huge swathe of political popular and public opinion - including charities and others making up Mr Cameron's 'Big Society' - wishing to see significant changes.
Ministers have already had to use procedural means and whipping to reverse seven other defeats over their proposals, which include capping benefits at £26,000 a year per household irrespective of need and on top of individual benefit caps.
Peers have been discussing a series of amendments to the legislation, and have been praised by welfare advocates for showing detailed attention to the legislation in a way that the elected House of Commons has, critics say, failed to match.
The latest amendment, tabled by crossbencher Lord Best, would limit the impact of a "bedroom tax", so that disabled people, war widows and foster carers with more than one spare bedroom would be exempt from a proposed £14 cut in housing benefit. It passed by 236 votes to 226, reports the BBC.
During the latest debate on 14 February 2012, Crossbench peer Baroness Meacher eventually withdrew her amendment calling on ministers to limit cuts to top-up payments made to the parents of disabled children. She did this after a government pledge to hold a review of the situation.
Lady Meacher told the House of Lords: "I do not accept this part of the bill is fair. It is not. It is deeply, deeply unfair."
Disability campaigners are carefully scrutinising government promises, and say they will push very hard to see that they are not broken or watered down. The Spartacus Report initiative on DLA, which has played a major part in raising the political temperature around the WRB, highlighting the government's attempt to get the most vulnerable in society to pay for its economic policy choices, is now forming into an ongoing grassroots campaign.
The use of Financial Privilege and other measures has been strongly criticised. Baroness Ruth Lister, a former professor of social policy and an acknowledged expert in the field, accused the government last night of being "sneaky" in its tactics.
A briefing on the Bill's implications for constitutional procedure, fiscal outcomes and second chamber reform has been written by 'Responsible Reform' (Spartacus Report) co-author Sue Marsh, and published online by the beliefs and values thinktank Ekklesia.
Yesterday Labour's Lord Morgan accused the coalition of trying to establish "a single-chamber Parliament in this country" so that its desires might implemented with less need to heed well-researched criticism.
Meanwhile, Baroness Boothroyd, a former Speaker of the House of Commons, asked for "negotiation and compromise" between the two Houses, "rather than for the government to behave in a heavy-handed manner".
Ekklesia is also briefing about the flawed Work Capability Assessment (WCA) process, in relation to processes proposed by the government for Personal Independence Payments, the substantially reduced and restricted partial replacement for Disability Living Allowance, which helps disabled people in and out of work cope with the extra costs of their circumstances in the face of a disabling society.
* Welfare Reform Bill: Financial privilege, constitutional convention, fiscal and second chamber reform implications, by Sue Marsh - http://www.ekklesia.co.uk/node/16280 
* Ekklesia's reporting, commentary, analysis and research on the WRB - referencing NGO and academic sources - is available in aggregated link form here: http://www.ekklesia.co.uk/welfarereformbill 
* Background, resources and links for the Spartacus initiative: http://wearespartacus.org.uk/ 
* Responsible Reform: Changes to Disability Living Allowance - http://www.ekklesia.co.uk/responsiblereformDLA