The world’s leading airline operators today dealt a body blow to the Mayor of London over plans to replace Heathrow with a new airport in the Thames Estuary.

A £40bn six-runway airport built on reclaimed land dubbed “Boris Island” would bury Heathrow’s third-runway expansion and trigger an end to flights over south-west London, with the airport’s ultimate closure.

But the Board of Airline Representatives UK - which makes up 90 per cent of Heathrow’s operators - said there was an insurmountable safety risk concerning the estuary’s bird colonies, which could strike aircraft.

British Airway’s chief executive, Willie Walsh, also claimed in a survey commissioned by Medway Council how closing Heathrow would create a “vast wasteland west of London”.

The survey’s findings are due to be presented to deputy Mayor, Kit Malthouse, tomorrow.

Former Wimbledon resident and co-founder of the Plane Stupid campaign, Richard George, said: “Boris Island is a great fantasy and we all have to have our crazy ideas, but this will do nothing to tackle climate change.

“What the idea does demonstrate, however, is that the Mayor of London will even look to building a whole new airport rather than agree to a third runway. Heathrow’s expansion is so disastrous to west London that we just can’t let it happen.”

Mayor Boris Johnson has championed the scheme as an alternative to Heathrow expansion. However the Conservative party’s leadership has distanced itself from the idea, first put forward in 2008.