Operator BAA says Heathrow airport is "jam-packed"
An airport on an artificial island in the Thames estuary could be the answer to the overcrowding at Heathrow, London's mayor has suggested.
Boris Johnson believes the island solution could put an end to the need for a third runway at Heathrow.
Officials are looking at plans to reduce air traffic congestion at Heathrow and focus on a 24-hour airport off the Isle of Sheppey in Kent.
Heathrow handles more than 500,000 take-offs and landings a year.
In his transport manifesto unveiled during the mayoral elections Mr Johnson had spoken about a possible new airport in the Thames estuary.
Mr Johnson said: "You can't endlessly expand Heathrow in the suburbs of west London and entrench what was really a planning error of decades ago.
"I'm looking at all the airports around the perimeter including the option of a new site somewhere in the Thames estuary, that's something I definitely think we should look at.
"What we are looking at is a way of solving this great capital's aviation needs without endlessly expanding our number one international airport," he added.
A spokesperson for the mayor said Mr Johnson "wants to undertake a study to establish the feasibility of the idea once and for all and is in the process of examining the best way to take the study forward."
Mr Johnson added that the environmental impact on the proposed site will also be considered while judging the site's viability.
Grahame Madge, a spokesperson for the Royal Society for the Protection of Birds, said Thames estuary is the feeding ground for "tens of thousands" of migrating birds.
"Any development proposed in an area that is internationally important for wildlife is a major issue.
"We would need to look at the proposals in detail, but it would be hard to see how you could locate an airport in an area so vital for birds without it being environmentally damaging."
John Stewart, from Hacan (Heathrow Association for the Control of Aircraft Noise) which opposes Heathrow's expansion, said: "The market in the South East couldn't support two major hub airports.
"It would need to be either Heathrow or an off-shore airport. But who is going to invest in a new airport with Heathrow just the other side of London?"
By the end of this year the government is due to make a decision on the proposed expansion of Heathrow.
Operator BAA has been stressing the need for expansion saying that Heathrow is "jam-packed" and needs a third runway to remain competitive globally.
But environmentalists, residents groups and councils opposing the move say the proposed expansion would have a serious impact on hundreds of thousands of homes in the area in terms of air quality and noise levels.