David Cameron is in "serious trouble" for neglecting to do more to save the union with Scotland - and relying on his old nemesis Gordon Brown to lead the campaign to stop Scotland becoming independent.
Conservative MPs are reportedly canvassing members to see if they have the backing for a no confidence vote in the event Scotland votes Yes on 18 September.
Polls show the two sides are neck and neck after a surge for the Yes campaign in recent weeks.
Cameron has had a minimal public role in the debate and now former prime minister Brown, whom Cameron faced across the ballot box in the Commons for nearly three years, is taking a lead to save the UK.
A source close to the 1922 Committee of backbench Tory MPs said Cameron was poised to "go down in history" as the man who lost the union.
"He is in a right hole. I think that he is in serious trouble. One of the reasons why I became a Conservative was a because of the union. We were the Conservative and Unionist Party," the source told The Daily Telegraph.
Meanwhile, Brown has laid out a timetable for more devolution in Scotland which the three main parties are expected to formally endorse today.
Daily Mail deputy editor Tony Gallagher said the paper's headline today was one "you would never expect".
Page 1: Cameron asks Brown to save the union - there's a headline you never expect.... pic.twitter.com/j3PzfMcvn6— Tony Gallagher (@gallaghereditor) September 9, 2014
It's ironic that the man who Cameron mocked for claiming he "saved the world" could now be the one to save the union.
In December 2008, Brown, then prime minister, claimed his government had saved "the world" while discussing the banking crisis during PMQs, prompting uproar in the House of Commons.
At the end of it, Cameron replied: "Well, it's now on the record. He's so busy talking about saving the world he's forgotten about the businesses in this country."