Liberal Democrat Business Secretary Vince Cable has said Heathrow expansion "will not happen" amidst a growing row over developing the airport's capacity.
"There is an absolutely clear coalition commitment not to expand Heathrow," he told the BBC's Andrew Marr Show.
"There is a very formidable political coalition against it: my party is totally opposed; Boris Johnson and the London Conservatives are opposed; the Labour Party seems to be moving against it."
Instead Cable insisted the commission set up by the government to "maintain the country's status as an international hub for aviation" will look into alternative plans.
"It is not going to happen, so the value of this commission the Prime Minister had been talking about is looking at alternatives," Cable told Marr.
A growing number of backbench MPs support the expansion of Heathrow, although the coalition agreement set up in 2010 included a commitment not to expand Heathrow.
However earlier this year senior Conservative Tim Yeo goaded David Cameron over the expansion of Heathrow airport, urging him to decide if he is "a man or a mouse".
The former environment minister, who chairs the Commons energy committee, insisted that environmental objections to calls for a third runway are disappearing and claimed backing the move would give the government a "sense of mission".
The Mail on Sunday reported that Tory MP Zac Goldsmith had offered his safe seat to Boris Johnson in a bid to stop plans for expanding Heathrow.
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.
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".
Boris's proposal for a new airport east of the capital on land in the Thames Estuary has led to his plans being nicknamed 'Boris Island'.
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."Suggest a correction