A Tory plot to oust David Cameron has been revealed by a backbench MP who confirmed he was asked to consider a “stalking horse” leadership challenge against the Prime Minister.

Colonel Bob Stewart said he was approached by two party colleagues before the summer recess with the proposal but that he told them to "get lost" and rejected the idea as "silly".

Details of the scheming was exposed by the Mail on Sunday which also reported that Tory MP Zac Goldsmith had offered his safe Tory seat to Boris Johnson.

Mr Goldsmith has vowed to resign as the MP for Richmond in south west London if the Government revives controversial plans for a third runway at Heathrow airport - which is also fiercely opposed by the London Mayor.

The newspaper said that the idea of Mr Johnson fighting the subsequent by-election to secure a return to the Commons and the chance to challenge for the leadership was made in talks to discuss how best to oppose the airport expansion.

The idea was said to have been dismissed "out of hand" by the Mayor, whose position as a potential challenger to Mr Cameron has been reinforced by the successful London Olympics.

Asked about the separate plot, Colonel Stewart, who was commanding officer of the British battalion in Bosnia, told the Press Association: "It was a silly suggestion that I dismissed. I told them to get lost.

"I was not having anything to do with it."

He declined to name the plotters and said he had not been told on whose behalf the pair were operating.

"I do not know; I do not care," he said, insisting he remained loyal to Mr Cameron who was "the reason I came into politics".

"I may have rebelled by voting against House of Lords reform and on Europe but that does not make me disloyal. He is the leader of our country, the leader of our party and I believe in loyalty."

The Mayor's official spokesman said: "It's no surprise that the Mayor has met and will continue to meet those who share his concerns over the lack of aviation capacity in London and the South-East.

"But the story in question is without doubt fanciful."

Mr Goldsmith told the newspaper: "I saw Boris this week and we compared notes on Heathrow to see what we could do to kill off the third runway.

"We covered all sorts of possibilities. I would do anything I need to deliver to my constituents what I said I would."

Mr Johnson, who has dismissed suggestions he could cut short his mayoral term to launch a leadership bid, has led the outcry over the reconsideration of Heathrow expansion.

He strongly criticised the reshuffle ousting of Justine Greening - who is also opposed to the move - as Transport Secretary and has expressed fears the Government plans a "stealthy U-turn".

Mr Cameron has ordered a cross-party commission to seek consensus on the divisive issue of airport capacity in south east England but has insisted he will not break a manifesto pledge ruling out a third runway at Heathrow during this Parliament.

The Mayor discussed the issue with the premier in the margins of a meeting this week of the high-profile committee overseeing the 2012 Olympic and Paralympic Games.

"It's no secret the Mayor opposes the building of a third runway, he was re-elected opposing any such notion, he'll continue to oppose any such notion, and he'll be doing it as Mayor of London," the spokesman said.

"The Mayor believes the Government's announcement of an Independent Commission has at least re-opened the debate on aviation capacity. That gives him the opportunity to demonstrate why Heathrow expansion isn't the answer, and the creation of a new 4 runway hub airport is. The Mayor will be doing both in the weeks and months ahead."