The RSPB and other environmental campaign groups have warned the Government against including a Thames Estuary airport in an upcoming consultation on the future of aviation.
David Cameron is set to announce an official consultation which will include plans for an airport hub in the Estuary, a haven for hundreds of thousands of wildfowl and wading birds.
As well as destroying this vital habitat, experts believe an airport here would be at high risk of bird strike, with very serious flight-safety implications.
RSPB conservation director Martin Harper, said: “There is no economic argument for destroying a vital habitat for thousands of wetland birds. We would be horrified if this act of environmental vandalism goes ahead simply to suit a short-termist approach to the economic mess we are in.
“Concreting over our natural environment and pumping more carbon into our atmosphere is no way to grow a long term sustainable future of our country.
“The last Government produced a white paper which looked at this idea and it concluded that it would be bad for business, bad for wildlife and bad for air safety. This Government now risks wasting public money in order to reach the same conclusion.
“The Estuary is not a wasteland waiting to be developed for the benefit of London, it is a jewel in our natural crown and is only there as a result of years of campaigning from local residents and conservationists.
“George Osborne has already made it clear that he feels environmental regulation protecting our most valuable wildlife sites is a brake on business. Weakening those rules would give environmentally destructive proposals like this an easy ride.
"After facing huge public opposition in response to proposed forestry sell-offs and the reform of England’s planning system, is the Government ready for a third major public uproar?”
Friends of the Earth's Executive Director Andy Atkins added: "A new airport in the Thames estuary would have a devastating impact on local communities and the environment - and all for pie-in-the sky economics that simply don't add up.
"London doesn't need another hub airport - the capital already has more flights to the world's main business destinations than our European neighbours.
"David Cameron's pledge to lead the greenest Government ever will ring hollow if he gives the green light to a huge expansion in air travel."
And the WWF says it is also deeply concerned by rumours that the coalition Government could be putting Southeast airport expansion back on the agenda. WWF believes this is neither necessary
A recent WWF report claimed there is already sufficient available capacity across London's six airports and seven runways to meet demand to 2050 without having to build a further airport, especially given the trend towards larger planes and higher passenger loading.
Add to this a decline in domestic flights, growth in train travel, greater use of videoconferencing and reduced business flying and it argued it is impossible to justify further expansion, especially as it would be likely to destroy the UK's chance of meeting legally binding climate targets.
Jean Leston, Senior Transport Policy Adviser, WWF-UK said: "The government long ago moved from an unsustainable "predict and provide" model for the UK's road network, when it became obvious that we could not simply build more roads for yet more cars.
“We need a similar shift in thinking for future aviation policy. Air travel is the UK's fastest growing source of carbon emissions. If we build a new runway or airport in the Southeast, we will be building the single biggest source of carbon in the country, at a time when we should be rapidly reducing our emissions."
"Heathrow already offers far more flights to 20 of the world's 27 top business destinations and more business routes than Charles de Gaulle and Frankfurt combined.
“The aviation industry is trying to create national hysteria about a need for expansion when they should be looking at the facts: Heathrow's doing just fine in terms of competitiveness and it won't take a £50 billion new airport completed in the distant future to improve our connectivity."