Zac Goldsmith has warned that a Government u-turn on Heathrow expansion would have “crushing political ramifications” for his party.

The outspoken Richmond Park MP made the comments amid claims senior Tories wanted to reconsider the idea of a third runway to help boost the economy.

Mr Goldsmith said this would be an “unbearable betrayal” for the 2m residents living under the flight paths and threatened to resign if the Conservative Party went back on its pre-election pledge to block Heathrow expansion.

He said: “For now, the Government’s position is clear; there will be no third runway.

“But I cannot in good faith discount the mounting rumours, and there does appear to be a movement within Government for a policy change.”

Vince Cable, MP for Twickenham, declined to say this week whether he would quit if the Government reconsidered a third runway.

The Business Secretary said he was “in a somewhat different position” to Mr Goldsmith, as the Liberal Democrats insisted they vigorously opposed Heathrow expansion.

He said: “He and I both feel strongly for this. I think his strong statement will be appreciated by local residents.

“He and I both strongly support observing the terms of the coalition agreement that there’s no third runway at Heathrow.”

Prime Minister David Cameron and Chancellor George Osborne have reportedly decided to re-examine Heathrow policy after business leaders warned trade would move elsewhere if the airport did not expand.

Mr Goldsmith said he believed the Heathrow controversy helped him win his Richmond seat, one of the biggest victories for the Conservatives in the 2010 election.

He said: “I do believe that a u-turn of this magnitude would have crushing political ramifications for both members of the coalition, whose pre-election opposition to the third runway was unambiguous.

“Political integrity is a highly valued but extremely limited commodity, and a betrayal of this sort would destroy what little trust there remains in politics.

“I pledged before the election to trigger a byelection in the event of a u-turn on the third runway, and it goes without saying that my position has not changed. I do not believe it will come to that, and I am reassured that many of my colleagues remain resolute in their opposition to the third runway.”

BAA withdrew its planning application for a third runway at Heathrow in May 2010 after the new coalition Government announced it had scrapped the plans in a joint policy agreement.

Colin Matthews, chief executive of BAA, indicated at the time the air operator would not give up, saying it continued to believe extra capacity would strengthen the UK’s trading links.