Expanding Heathrow airport would cause a split at the very top of government, says a newly re-elected Tory MP.
Zac Goldsmith, a long-time critic of the scheme, repeated his threat to resign if the government agrees to build a new runway in west London instead of further south at Gatwick.
Mr Goldsmith was re-elected as MP for Richmond Park in south-west London.
His resignation would trigger a by-election in which he could stand as an independent on that one issue.
It would offer him the opportunity to make a lot of noise. This is a man who has only just been voted back into his seat with a hugely swollen majority, adding nearly 20,000 votes.
"I made that promise in 2008 and it still stands," Mr Goldsmith told the BBC. "It's not something I want to do, but it's something I'd have to do."
The independent Airports Commission should hand over its final report next month, picking either Heathrow or Gatwick for expansion.
After that, it will be down to David Cameron's fledgling government to decide whether to go along with that recommendation or pick their own.
But Mr Goldsmith thinks that selecting Heathrow could spell disaster for the prime minister,
"If you look at the cabinet today, there are at least three heavyweight people there, Philip Hammond [Foreign Secretary], Justine Greening [International Development Secretary] and Boris Johnson [Member of Political Cabinet] and others, in fact, who are implacably opposed to Heathrow expansion," he said.
"He'd face a split at the highest level and I don't think a fragile government with a small majority wants to do that."
The MP also claims it would be "an off-the-scale betrayal" from Mr Cameron, who he says came to west London before the 2010 election and promised locals, "No ifs, no buts, the Conservatives won't expand Heathrow."
On Tuesday, another high-profile critic of Heathrow expansion, Boris Johnson, said he would not resign if the government picked the scheme. Instead, he would fight it from within.
All sides of the airport debate are ramping up the rhetoric ahead of Howard Davies' final report.
There is a growing feeling among people I speak to that he will plump for Heathrow, which is thought to be favoured by the Chancellor, George Osborne.
But having said that, both Gatwick and Heathrow seem to have their tails up, thinking they have successfully made their case for a new airport.
Another theory doing the rounds is that Howard Davies will pick Heathrow, but leave the door open for Gatwick to make life easier for the politicians.
Mr Goldsmith is not convinced: "I don't think he's in the market to produce a fudge... I think he wants an answer that'll be relatively clear."
"A year ago, I would have said Heathrow expansion's in the bag, but I think that he seems to have heard the arguments... and if I had to put my house on it, I'd say he's not going to recommend Heathrow expansion. But it's at best 51-49, no-one knows."
Two and a half years ago, the government set up the Airports Commission to offload an issue that was unsticking a nascent coalition. The Lib Dems, in particular, were struggling to get any expansion past their members.
They've gone now, and having sent the issue circling for years, it is coming in to land in the Conservatives' lap.