The Government has suffered a massive defeat in the House of Lords over its controversial welfare reform plans.
Peers voted by 270 to 128, majority 142, to prevent the Government charging single parents for using the Child Support Agency (CSA).
The successful amendment was put forward by Tory former lord chancellor Lord Mackay of Clashfern and received wide support from Conservatives and Liberal Democrats as well as from Labour peers.
His move would stop an upfront charge of £100 or £50 plus a levy of up to 12% on maintenance payments applying if a single parent, generally a mother, had taken "reasonable" steps to get the other parent to come to a voluntary agreement on child support.
The defeat was the sixth ministers have suffered on the Welfare Reform Bill, which is on its final day of report stage in the Lords. On Monday peers agreed an amendment from the Bishop of Ripon and Leeds, the Rt Rev John Packer, to remove child benefit from the £26,000-a-year cap on household benefits.
Lord Mackay said the Government's plans could put single mothers off seeking the support they were entitled to.
He said: "The motivation for these charges is said by the Government to be to bring people to voluntary agreement. I am entirely in favour of that but if that proves impossible where the woman is at the stage where there is nothing more she can do, the only thing she can do is pay."
The defeat might be overturned when the Bill returns to the Commons next month, but given the what appears to be a large rebellion among Tory and Lib Dem peers, the Government may be forced to offer concessions.
Government spokesman Lord De Mauley, urging peers not to back Lord Mackay's amendment, argued it would require the state "to try to arbitrate" on whether a parent had taken reasonable steps.
He said parents could challenge the decision and it would add to the "cost and complexity" of the system. Even if parents were allowed to offer a "self-declaration" that they had taken all reasonable steps, the scheme would cost £200 million to the end of March 2019, he said.
