David Cameron's hopes of fighting the 2015 general election on redrawn constituency boundaries were dealt a death blow in the Commons after the Liberal Democrats turned on their coalition colleagues.
MPs voted by 334 to 292, majority 42, to delay the review of the boundaries until 2018 after Deputy Prime Minister Nick Clegg withdrew his party's support for Mr Cameron's plan in retaliation for the failure to make progress on House of Lords reform.
In an unprecedented move reflecting the split between coalition parties on the issue, the Prime Minister agreed to suspend the requirement for Government ministers to exercise collective responsibility for the vote on the Electoral Registration and Administration Bill.
The Prime Minister had hoped the new constituencies would be in place for the next election, which could have resulted in up to an extra 20 seats for his Conservative Party.
But MPs accepted an amendment made by peers to the Bill which delays the review until after the next general election.
The plan would have seen the number of MPs reduced from 650 to 600, with constituencies of roughly equal numbers of voters.
But the amendment tabled in the Lords by a cross-party alliance led by Labour's Lord Hart of Chilton and Lib Dem Lord Rennard and now agreed by MPs has left the proposal in tatters.
Commons Leader Andrew Lansley pleaded with MPs to reject the change, arguing that it breached parliamentary conventions.
He said the Hart/Rennard amendment was "not only an abuse of parliamentary process, it is a democratic travesty".
"The unelected House is seeking to frustrate the previously expressed will of this Parliament, not a previous parliament, to deny fairness and equality in the franchise and fundamentally to manipulate the basis on which this House is to be elected," Mr Lansley said.