Changes to constituency boundaries that will help the Conservatives secure a majority at the next election will be blocked by the Liberal Democrats if Tory MPs torpedo plans to reform the House of Lords, a senior Lib Dem has warned.
In an interview with The Independent, Richard Reeves, Nick Clegg's director of strategy, said there would be "consequences" if up to 100 Tory MPs defeat the programme motion for the House of Lords Reform Bill.
The vote on Tuesday will determine how long MPs can debate the proposals for a 80% elected chamber for, with opponents of the reforms hoping to drag out the debate for as long as possible in order to scupper the Bill.
Labour are likely to vote against the programme motion and could successfully defeat the government if joined by a significant number of Tories.
"It is a very serious moment for the government," Reeves told the paper. "The vote is hugely significant. It is the critical moment for Lords reform, a once-in-a-generation chance to secure it."
Reeves has stepped down from his job with the deputy prime minister yesterday in order to move to the United States with his family.
In a parting shot at the Tories, Reeves said if Tory rebels conspired to ruin plans to reform the Lords then Lib Dems would take revenge.
"The idea that failure to deliver a government commitment on Lords reform would be consequence-free is for the birds," he said.
Under the provisions of the Parliamentary Voting System and Constituencies Act 2011, the number of MPs will be cut from 650 to 600.
The move will see the electoral map re-drawn in such a way that would be likely to benefit the Conservatives, however the final boundaries are yet to be approved by MPs.
Sadiq Khan MP, Labour’s shadow justice secretary, said the apparent behind the scenes wrangling strengthened the case for a referendum on the issue.
"This shows that major constitutional changes are in fact being done behind closed doors. There is now an even stronger case for letting the public have their say via a referendum," he said.
"The Government should not be ramming this legislation through Parliament without proper debate. That is why we are voting against the programme motion."
Senior Lib Dem MP David Laws sought to play down the prospects of a clash with Conservatives over the timetable for the Bill.
He said that both parties had included a commitment to Lords reform in their manifesto's at the last general election.
"These were commitments made by Conservative MPs as well as Lib Dems and we expect the vast majority of coalition MPs to support this and we expect it to go through next next week," he told Sky News.
While Tory backbencher Peter Bone, who is no fan of Lib Dems, said the Conservatives should pull out of the coalition and govern as a minority government.
Asked whether he was worried about threats from the Lib Dems he said sarcastically: "Quaking in my boots at the threat from the liberals, they just cant be trusted."
"The deal was they got this wretched AV vote in return for the boundary review," he said.