Zac Goldsmith has repeated his threat to quit as Richmond Park MP if the Government approves the third runway at Heathrow.

It has been widely speculated the Government will back the plans in the next two weeks, although Mr Goldsmith asserted that it was ‘not going to happen’.

Mr Goldsmith has previously said he would stand down as MP if Heathrow was allowed to expand, although he later told journalists he regretted that decision.

Mr Goldsmith told BBC Radio 4 on Friday that his position was ‘unchanged’.

He said: “I promised my constituents before I was ever elected in 2010 that I would trigger a byelection were the Government to give a green light to Heathrow expansion.

“My position has never changed.

“I’m committed to my constituents; I’m committed to fighting this campaign and I’m committed to winning this campaign.

“I have every confidence that will happen.”

He also said there were ‘huge question marks’ over whether a third runway could be delivered by Heathrow.

Mr Goldsmith said: “The legal risks are immense.

“You’ve got councils under the flight path lining up with big cheque books waiting to challenge these proposals.

“There are huge planning risks. There are financial risks. Heathrow is over-leveraged already.

“There is no prospect of them being able to raise the finance necessary to deliver this project without turning to the taxpayer.

“Whatever the Government decides, this project is not going to happen.”