Zac Goldsmith withdraws pledge not to stand as a Conservative if Cameron backs Heathrow

The Conservative favourite to be the next mayor of London has insisted he will remain in the party, even if the government backs expansion of Heathrow.

Zac Goldsmith has previously promised not to stand as a Conservative MP if his party backed a third runway at Heathrow.

He said two years ago that he "certainly wouldn't stand as a Conservative" if a pledge to expand Heathrow was in any future party manifesto.

"If the government changes its position on Heathrow expansion I will trigger a by-election, and if it happens in the manifesto of the next election then I certainly wouldn't stand as a Conservative," he said in 2013.

However, the Richmond Park MP said last night that while he would trigger a by-election in his parliamentary seat under those circumstances, he would still stand to be mayor under a Conservative banner.

"I would not resign from the Conservative party. I would not resign from the mayoral contest," he told the Conservative hustings at the Institute of Directors in central London.

"If there was a question mark over that I wouldn't be here today."

The Davies Commission backed the expansion of Heathrow earlier this year and there are signs that the government are moving towards supporting a third runway.

However, Goldsmith said he would continue to fight Heathrow expansion as mayor.

Goldsmith also softened his position on airport expansion elsewhere in the South East, suggesting that he might be persuaded to back another runway at Gatwick or elsewhere in order to increase "competition" with Heathrow.

However, he ruled out backing Boris Johnson's plan for a new hub airport in the Thames Estuary.

He dismissed calls from his rival candidates Andrew Boff and Stephen Greenhalgh to back the airport, saying that there were only a handful of MPs in Parliament willing to get behind it.

"None of us are Boris Johnson and [if even] Boris Johnson with his vision, power and influence in government was not able to generate more than a tiny level of support for it…

"Without cross party support, without deep support in Parliament it hasn't got a hope of getting off the air."