The Conservative candidate and current London mayor said that proposals to build a third runway at Heathrow would pose “an environmental disaster” and would be like trying to “cram a quart into a pint pot”.

Although Johnson has consistently opposed a third runway at Heathrow, he is an avid supporter of plans to construct a new airport hub on the Thames estuary.

Of the idea of a third runway at Heathrow – which is said to be being re-examined by David Cameron and George Osborne as they try to boost economic growth – “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.

“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 [transport secretary] Justine Greening’s consultation this summer.”

Ken Livingstone, the Labour mayoral candidate and former London mayor, is generally opposed to expansion in Greater London, but has not ruled out expansion at Stansted. He has also outlined plans for a “Crossrail 2 and 3”, providing more rail services across the capital to link with trains coming into London.

Picture: Getty