Tories have rounded angrily on Liberal Democrat peers after they combined with Labour to inflict a bruising defeat on David Cameron's plans to redraw parliamentary boundaries.
The House of Lords voted by 300 to 231 - a majority of 69 - to back an amendment delaying plans for a boundary review and to cut the number of MPs from 650 to 600 until 2018 at the earliest.
Six of the seven Lib Dem frontbenchers in upper chamber joined the revolt - the first time in this Parliament that ministers in either House have voted against the Government. The seventh, Lord Wallace of Saltaire, a Lib Dem whip who is responsible for taking the legislation through the House, did not vote. In all, 72 Lib Dems voted against the Government with none voting in favour.
Deputy Prime Minister Nick Clegg made clear over the summer that the Lib Dems would seek to delay the boundary changes - which experts believe could be worth 20 extra seats to the Conservatives at the next general election - after being forced to abandon plans to reform the House of Lords in the face of Tory opposition.
But that did nothing to lessen the anger among Conservatives, with former cabinet minister Lord Forsyth of Drumlean accusing them of "cheating". He pointed out that Tory parliamentary aides in the Commons had been sacked for voting against Lords reform.
"You don't take the Queen's shilling and then go through the lobbies and vote against the Prime Minister," he said. "It is an absolute disgrace."
Fellow Tory Lord Dobbs accused Mr Clegg of exacting revenge on his coalition partners because of his failure on Lords reform. "The truth is that this is solely, sadly and cynically because the Deputy Prime Minister didn't get his way on House of Lords reform," he said. "Now he wants to exact a little retribution. It's nothing less than a great political sulk."
Home Office minister Lord Taylor of Holbeach said the amendment to the Electoral Registration and Administration Bill was "conceived in mischief" and motivated by "hubris and cynicism".
However the senior Lib Dem peer Lord Rennard said the Conservatives should not be surprised at the vote. "In countries across Europe where coalition is much more the norm, it is much more normal and people understand that different parties vote in different ways on some issues while agreeing on packages of measures where they can find agreement in what they both consider to be in the national interest," he said.
There was particular anger on the Government benches that supporters of the amendment pressed ahead despite a ruling by the clerks of the House that it was "inadmissible" as it was not relevant to the Bill. Mr Cameron will have to decide whether to try to overturn the amendment in the Commons - although with no overall Conservative majority in the lower chamber the parliamentary arithmetic would appear to be against him.