The government has suffered a fresh defeat in the House of Lords over its welfare reforms, as peers backed plans to limit the "bedroom tax" on social housing tenants with spare rooms.
The government wants to reduce housing benefit payments for council tenants who live in properties with spare rooms.
But peers voted by 236 votes to 226 - majority 10 - to exempt disabled people, war widows and foster carers from the proposed £14 cut in payments if there is no suitable alternative accommodation available.
The move, proposed by crossbench peer Lord Best during peers' consideration of MPs' amendments to the Welfare Reform Bill on 14 February 2012, is expected to cost £100m.
The defeat means the bill must be sent back to the Commons, where the government is likely to seek to overturn the amendment.
Both Houses have to agree on the final contents of a bill before it can become law.
Earlier this month, the Commons voted to reject peers' changes to the bill during its passage through the upper chamber.
The government announced it would use parliamentary rules known as "financial privilege" to prevent the Lords from reinstating their amendments.
But this prompted widespread concern from peers on all sides of the House who feared it would prevent parliamentary "ping pong" over certain aspects of the legislation.
At the start of the debate, the leader of the House, Lord Strathclyde, told peers it was "perfectly in order" for them to discuss the amendments again, but he warned "it is simply unprofitable to send back to the Commons" amendments which would also be ruled to affect the Commons' financial privilege.
The government then offered a series of concessions to peers in an attempt to avoid a stand-off over its welfare plans.
Crossbencher Baroness Meacher agreed to drop an amendment to limit cuts to top-up payments made to the parents of disabled children, following assurances the government would review the way severely disabled children are treated in the transition to its proposed new welfare system.
Peers also agreed not to insist on several of their amendments relating to eligibility for Employment and Support Allowance.
Later analysis of the vote on Lord Best's amendment showed there were six Liberal Democrat rebels: Lord Avebury, Lord Kirkwood of Kirkhope, Baroness Miller of Chilthorne Domer, Lord Smith of Clifton, Baroness Tonge and Lord Tordoff.
The amendment was also backed by 58 crossbenchers, two bishops, 162 Labour peers and eight others.
the government won a vote on a Labour amendment seeking to regionalise plans for an annual cap on housing benefits.