A senior Conservative MP has said it is "very likely" the coalition will break up as much as a year before the 2015 general election, hours after David Cameron urged warring Tories and Liberal Democrats to remain united.
Graham Brady, the chairman of the influential backbench 1922 committee of Tory MPs, said he expected a "moment of separation" would become necessary in the run-in to the election much sooner than previously thought.
"I guess looking six months or even a year ahead of the general election we should be speaking far more about what our own intentions as a political party are," he said.
Speaking to the BBC's Westminster Hour on Sunday evening, Brady said the prime minister and other Tories should already be articulating what a majority Conservative government would do, despite having to govern with the Lib Dems for almost three more years.
And while he said he was not advocating the immediate end to the Lib-Con government, he said there was "a need for the parties to plan the process of exit from the coalition".
Brady also told the BBC that he did not think the 91 Tory MPs who voted against the Lib Dem's "hobby horse" plans to reform the House of Lords would agree to any compromise agreement that included elections of any sort.
"A great many colleagues on both sides of the House of Commons have a principled concern with the introduction of an elected element," he said.
It has been suggested that a deal could be reached that sees the remaining 92 hereditary peers replaced with elected Members in 2015.
But Brady added: "It's certainly difficult to see most of the 91 Tory members and a good many of those on the Labour benches shifting their ground on what for them is a really fundamental obstacle."
Much of the argument between the Lib Dems and the Tory rebels has been over what was specifically agreed to in the coalition agreement.
The Lib Dems say the Tories should be true to their word and support legislation to reform the Lords.
However the Tory rebels say the agreement merely committed them "to bring forward proposals for a wholly or mainly elected upper chamber" - not to actually vote for one.
Lib Dem Stephen Williams told Westminster Hour this was an attempt to "wriggle out" of the deal. "This was meant to be a whipped issue where both parties would deliver this," he said.
It had been suggested that the Lib Dems and Conservatives would seek to renew their joint government half-way through the term with a fresh programme for government known as 'Coalition 2.0'.
However in an interview with The House magazine last week, David Laws, one of the key Lib Dem architects of the initial document hammered out in the days after the inconclusive 2010 election, confirmed that this was not on the cards.
"It’s more or less been decided," the Yeovil MP said. "That the idea of having a separate coalition agreement is really not necessary."
"The original coalition agreement was fantastically ambitious.... focusing on those things and delivering those big things would be far more important than coming up with a lot of small, diddly additional policies that would simply distract us."
Writing in The Sunday Times yesterday, Cameron said it was essential that differences over Lords reform did not stop Lib Dems and Tories working together in government in the national interest.
"These differences matter and at the next election they will help define us. But we're not in an election, now. We're not even close," he said.
Cameron and Clegg are due to make a joint appearance today in a show of unity to announce £9bn worth of rail investment.
However the fallout from last week's rebellion against Lords reform by Tory backbenchers continued over the weekend, with senior Lib Dems to warning them there may be consequences.
Lib Dem Foreign Office minister Jeremy Browne told the BBC's Sunday Politics that Tory rebels should remember the government was a coalition not a majority Tory administration.
"Some Conservative backbenchers behave as if they did win the general election," he said.
And the party's former leader, Sir Ming Campbell, told the BBC's Marr programme on Sunday that his colleagues would find it very hard to support the changes to the electoral map if Tory backbenchers killed off reform of the House of Lords.
He said: "If you’re a Liberal Democrat Member of Parliament whose seat has been pretty substantially carved up as a result of the proposals for a review of the boundaries, then the idea that you would simply march into the lobbies in support of the Conservative government’s particular anxiety to obtain this piece of legislation is one which may be very hard to swallow."
The planned changes to the constituency boundaries that would see the the number of MPs cut from 650 to 600 is thought to be electorally advantages to the Conservative Party and would make it much easier for them to win an outright majority at the next election.
But in a sign that tensions run deep despite the prime minister's call for unity, backbencher Stewart Jackson tweeted on Sunday: "Memo to bolshy Lib Dems: Break deal on boundary changes & you'll be out of govt the next day and maybe 4ever. That vote has consequences too."
And in a sign Cameron may have to watch his back if he surrenders the boundary changes, Jackson added: "Idea that PM can just 'gift' Lib Dems voting against boundary changes is nonsense. If he allows this, discipline in the party will evaporate."