David Cameron faces a momentous challenge to hold his troops together if he negotiates a deal with Nick Clegg, Tories from all wings of the party warned last night.
Opposition has been growing to suggestions that Mr Cameron could give ground on electoral reform in order to form a coalition with the Liberal Democrats.
The discontent has been exacerbated by discontent among some MPs over the style of the election campaign, which saw the party fail to make the historic breakthrough forecast by the polls just six months ago.
The Tory leader's negotiating team has been bluntly told that it would win little support for any move towards scrapping the first-past-the-post voting system.
One Shadow minister told The Independent last night: "The PR element is causing a great deal of angst both among MPs and within the grassroots. We are seeing the clearest evidence of the arguments against it at the moment – we would have chaos at every election as people scrambled around trying to do a deal."
Lord Heseltine, the Tory former deputy prime minister, told the BBC yesterday: "I don't think for a minute that David Cameron will concede change to the voting system and I don't think that he needs to. His position is much stronger than I think the commentators give credit for."
Graham Brady, who is favourite to become the new chairman of the Conservative backbench 1922 Committee, said: "Certainly my inclination is more towards seeking to operate as a minority government bringing in the support of others where it exists and where there is a consensus that can created. I think that is probably, generally, the mood of colleagues." Mr Cameron faces powerful opposition within the Shadow Cabinet and on the Tory backbenches towards any threat to the current voting system.
Liam Fox, the shadow Defence Secretary, has warned that the issue did not arise once when he campaigned during the general election.
Daniel Kawczynski, the Conservative chairman of the All-Party Group for First Past the Post, has also argued that it was not the time for Parliament to be discussing electoral reform, when Britain was facing one of the worst economic crises in its history. His view is very widely shared on the Tory benches, as well as by many Labour MPs.
For many Conservative MPs across the south of England, the Liberal Democrats are the main challengers in their constituencies, so a link-up with their rivals would be a bitter pill to swallow. Tory right-wingers are also fiercely hostile to Liberal Democrat policy on the European Union, immigration and defence.
Such are the policy differences that some activists believe Mr Cameron should ignore the Liberal Democrats and form a minority administration, perhaps involving a coalition with the eight MPs from the Democratic Unionist Party.
The former party chairman, Lord Tebbit, even claimed yesterday that a deal with the Liberal Democrats would mean Tory plans to force through spending cuts to tackle the national debt would be watered down. He argued that a minority administration was preferable to a coalition, because a second election was inevitable anyway.
"Mr Cameron has dissipated a 20 per cent lead in the polls, he has love-bombed the Lib Dems and said he is the heir to Blair," he said. "That wasn't helpful in winning the election. I have gone along with what Mr Cameron wanted because he is the leader.
"I will support him if he sticks to his manifesto. If he was pushed around by a minor party leader into abandoning things in the Conservative manifesto, it would be daft."
Some Conservatives are even arguing that it might be preferable to walk away from the Liberal Democrats and allow Gordon Brown to stitch up a centre-Left coalition that would tear itself apart when confronted with the cuts required to slash the deficit.
Mr Cameron has also come under fire for failing to involve more senior Tories in the negotiations with the Liberal Democrats.
In an attempt to rebut the accusation, which is strongly denied by party officials, he will address the 1922 Committee today. He will also hold an "open house" in his office to meet Conservative MPs and hear their concerns.
A former Foreign Secretary, Malcolm Rifkind, said he would be "astonished" if he could not accept any proposals put forward by his leader.
"What I do see is a good body language. They seem to be talking seriously," he said, adding that both sides were aware that prolonged uncertainty could have "serious implications for our credit ratings, our interest rates".
Earlier, Michael Gove said: "We must be respectful of what the Liberal Democrats want to do. We're not attempting to sandbag or manoeuvre them into a situation with which they are unhappy."
He said he was prepared to give up his potential position as Education Secretary for a Liberal Democrat. Currently, David Laws is the Liberal Democrats' education spokesman.
But an unnamed Tory MP told a Sunday newspaper: "The arrogant little gang around Cameron are smug and dismissive of their own MPs and we have all paid the price.
"The manifesto was a policy-free zone and, surprise surprise, the public was reluctant to vote for us. Now we have to grovel to the Lib Dems to get Labour out. It is a joke."
Tim Montgomerie, editor of the influential ConservativeHome website, wrote on his blog: "The Conservative leader was careful to call Michael Howard, Iain Duncan Smith and other senior Tories before yesterday's invitation to the Liberal democrats.
"He certainly needs to be aware that the party is psychologically in a weak place."
David Cameron's juggling challenge
Led by David Cameron, Michael Gove and Oliver Letwin, they believe that some accommodation with the Liberal Democrats is essential to form a stable government and also demonstrates the party's willingness to change – and to be seen by they electorate as having done so. However they are determined not to give much ground over electoral reform.
Led by Liam Fox and William Hague, they are deeply suspicious of Liberal Democrat intentions over Europe, defence and immigration. They baulk at even the most minor concessions over the voting system, but would countenance a deal on their terms. Mr Cameron's decision to appoint Mr Hague as the party's main negotiator with the Liberal Democrats shows the importance of keeping this wing of the party on-side.
The traditionalist right
Led by Norman Tebbit, David Davis and Edward Leigh, they are just as hostile to the Liberal Democrats as Labour – and are prepared to say so openly. They instinctively would prefer Mr Cameron to go it alone, or perhaps with Democratic Unionist backing.
The traditionalist left
Led by Kenneth Clarke and Michael Heseltine, they may have some sympathies with the Liberal Democrats, but they grew up in an era when the Liberals were irrelevant. Lord Heseltine wants Mr Cameron to go it alone. However, the Tory left is unlikely to undermine Cameron for fear of giving strength to their real enemies on the right of the party.
They think it best to let Gordon Brown form a "rainbow coalition" and see it crumble, paving the way to a Tory landslide in a year or so. None dare voice their views publicly – yet.
The proportional representation fans
Sadly for the Liberal Democrats, these are few and far between. Douglas Carswell is the only one so far to have called for first-past-the-post to be scrapped.