Boris Johnson insists there will be no third runway at Heathrow

Boris Johnson has insisted he would not allow a third runway to be built at Heathrow Airport (AP)

Boris Johnson has insisted there will not be a third runway built at Heathrow, despite the Prime Minister and Chancellor stating the need for airport expansion in south east England.

The Mayor of London said a third runway would be “intolerable” for those living to the west of the capital, calling it a potential “environmental disaster”.

Johnson, who is running for re-election as London Mayor in May, said: "[A third runway] would mean a huge increase in planes over London, and intolerable traffic and fumes in the west of the city - and it will not be built as long as I am Mayor of London."

As part of their 2010 manifesto, the Conservative Party explicitly ruled out the prospect of a third runway. But there are now reports that senior Tories are looking into the prospect of developing RAF Northolt to fill the role.

The single-runway RAF station sits six miles north of Heathrow, and is already used for some private, non-military flights. During the construction of Heathrow, RAF Northolt was the temporarily the busiest airport in Europe.

Last week David Cameron said that the UK must retain its status as a major global hub for air travel, although he acknowledged the issue was "controversial".

Cameron said: "I'm not blind to the need to increase airport capacity, particularly in the South East."

"We are acting now to make the best use of existing capacity - Gatwick is emerging as a business airport for London, under a new owner competing with Heathrow” he added.

Tim Yeo, the Tory chairman of the Commons Energy and Climate Change Committee, has called for the Conservatives to revisit their Heathrow policy, saying he has "completely changed" his mind on the issue.

Speaking to The Observer newspaper, he said: "We cannot wait around any longer. We have to get on with this. If we don't the Chinese and others will take their business elsewhere...I think there is a major rethink going on, and there needs to be."

Zac Goldsmith, the environmentalist and Conservative MP for west London’s Richmond Park and North Kingston constituency, threatened to resign his seat and force a by-election if the Government went back on its promise not to expand Heathrow. He said any such move would represent a "betrayal".