I won't allow third Heathrow runway, says Boris Johnson Boris Johnson has insisted he would not allow a third runway to be built at Heathrow Airport, amid speculation that senior Tories want to revisit the idea. The Conservative Mayor of London, fighting for re-election in May, said the move would be an "environmental disaster" and "intolerable" for people in the west of the capital. The Tories ruled out the prospect of a third runway in their 2010 manifesto, but both Prime Minister David Cameron and Chancellor George Osborne last week acknowledged the need for airport expansion in the South-East. Mr Cameron said the Government was prepared to consider the possibility of a new airport in the Thames Estuary, an idea that has been advanced by Mr Johnson and dubbed the "Boris Island." But there were reports that Mr Cameron and Mr Osborne were prepared to look again at options for Heathrow, in a move that would anger their Liberal Democrat coalition partners and Tory MPs in west London. One possibility was said to be to develop RAF Northolt, which is about six miles from Heathrow, into an effective third runway. Tory sources insisted that their commitment not to build a third runway remained. Transport Secretary Justine Greening is to set out plans on aviation in the summer. Mr Johnson, who faces serious damage at the polls if he becomes associated with plans for a third runway, said Heathrow could not be "endlessly" expanded. A third runway would be an environmental disaster. It 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," he said. That is why the Government is right to look at all new solutions for extra aviation capacity except the third runway at Heathrow. I look forward to engaging with Justine Greening's consultation this summer. 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. He told The Observer it was vital to ensure South East England remained a global transport hub - a major concern for British business. 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. He added: "I think there is a major rethink going on, and there needs to be." Zac Goldsmith, the environmentalist and Tory MP for the west London constituency of Richmond Park and North Kingston, threatened this weekend to resign his seat and force a by-election if the Government reneged on its promise not to expand Heathrow. He said any such move would be a "betrayal." The Prime Minister said last week that the UK must retain its status as a major global hub for air travel, although he acknowledged the issue was "controversial." A spokeswoman for Ken Livingstone said: "Reports that Boris Johnson's Tory government are considering this show the Tory Mayor's claims to have successfully lobbied against the third runway are hollow and that people who voted Conservative on this basis have been betrayed. Tory Boris Johnson has done nothing while his Tory government pursue policies which will affect the quality of lives of millions of Londoners.