A Tory rebellion against Liberal Democrat proposals to reform the House of Lords could have serious repercussions for the coalition, a senior aide has claimed.
Richard Reeves, a senior aide to Nick Clegg, told The Independent that Liberal Democrats would retaliate with a rebellion against proposed boundary changes.
Reeves said the vote represented "a very serious moment for the Government", while the Lords vote represented a "once-in-a-generation chance".
The House of Commons will vote on Lib Dem proposals for a mainly elected upper chamber, with the vote expected to go to the wire.
Conservative backbenchers may choose to join with Labour in a vote against a motion limiting debate on the proposals, thus pushing the timetable back.
Reeves warned: "There would be broader consequences for the Government's programme, particularly around political and parliamentary reform.
"The idea that failure to deliver a government commitment on Lords would be consequence free is for the birds."
The Conservatives hope to gain as many as 20 seats at the 2015 general election following boundary changes that will cut the number of MPs by 50.
The Lords reforms have been heavily criticised, with concerns that they will prove too costly and will dilute the primacy of the House of Commons, and could clogg the wheels of government.
Labour supports the reform in principle, but appears set on a path to disrupt the timetable in a political manoeuvre.
The Torys have argued that the coalition made a deal for boundary reforms in exchange for Clegg's failed attempt at a voting referendum , but Reeves said: "Anyone who thinks Nick Clegg will shrug his shoulders [after a defeat], say 'never mind' and 'everyone tried our best', will be in for a rude awakening. That is not going to happen."
He denied the possibility of the Lib Dems walking out of the coalition, but his comments reflect the party's hunger for a win, with their support following its failure to push through voting reform and the u-turn on tuition fees.