LONDON will be known as the ‘city of planes’ if Heathrow starts work on a third runway, former Mayor Boris Johnson has claimed.

The Foreign Secretary and Uxbridge and South Ruislip MP is a long-time outspoken critic of Heathrow expansion, mooting an alternative scheme – dubbed 'Boris Island' – to build a new airport for the city on the Thames Estuary.

Fellow Conservative Zac Goldsmith, who ran to succeed Mr Johnson as London Mayor, has already announced he will step down as Richmond Park MP and trigger a by-election, following the decision of the airport sub-committee at Downing Street this morning.

Mr Johnson thanked Prime Minister Theresa May – who was previously an opponent of Heathrow expansion – for allowing him to speak out on the issue.

And he reiterated his belief that the process – which is now subject to public consultation before a Parliamentary vote in 2017 or 2018 – will be dragged out with a succession of legal challenges.

“No other world city would dream of subjecting hundreds of thousands of people to the levels of noise pollution that a third runway would,” he said.

“I worry that down the line, if and when this might happen, there would be an overwhelming clamour to build a fourth runway before it had even been completed.

“And what would London be like then? You’ve got New York as the city of beautiful skyscrapers, Paris is the city of light and London would be the city of planes. Is that really want we want?

“The day the bulldozers appear is a long way off and there are four Conservative led councils that will litigate against it and my view is the whole thing will be snarled up in objections and protests.

“This will create an erosion of the quality of life for local residents, it will be a hell of aircraft noise.”

Heathrow’s principle rival was Gatwick, where a second runaway was proposed, but Mr Johnson insists his own plans for a new airport remain the most viable, despite being dismissed by industry experts.

“In my time at City Hall we put forward alternative plans for a four runway 24 hour hub airport that would launch this country aboard and give us fantastic connectivity,” he added.

“If we’d got going then we’d be half or two thirds of the way down the track. In the long run we will have to go back to those ideas. Heathrow is not in the right place and a third runway is undeliverable.

“However, I’d like to thank the Prime Minister for allowing her colleagues to be able to express their views but I do think that building a third runway, slap bang in the middle on the western suburbs in the greatest city on earth, is not the right thing to do.”