Plans to build a 24-hour £39bn hub airport on large sandbanks off the Kent coast have been unveiled.
Engineering firm Beckett Rankine wants to construct a four-runway airport on Goodwin Sands near Deal.
Director Tim Beckett said it was the "most sustainable solution" to aviation expansion in the South East and would have the "least adverse impact".
The plan for the hub airport, the fourth proposed for the South East, is being opposed by environmentalists.
The Goodwin Sands are a series of shifting sandbanks, 11 miles long and six miles wide, that are also the site of historic shipwrecks.
Beckett Rankine said the location could support a 24-hour airport with four runways and did not have the environmental and logistical issues that came with proposals for an airport in the Thames Estuary.
It said the site would be linked to London by the existing HS1 high-speed rail line, the A2 and M20 and to Europe via the Eurostar service.
Mr Beckett said: "If the Davies Commission endorses the long-term requirement for a new, four-runway hub airport for London, then locating it at Goodwin will have the least adverse social and environmental impact of any option. It is certainly the most sustainable solution available.
"Creating a new airport for London presents a major regenerative opportunity. We believe that East Kent is an area that could benefit most from the boost of new jobs and economic uplift."
Daniel Moylan, aviation adviser to Mayor of London Boris Johnson, said: "The mayor has been encouraging proposals for a new airport to the east of London and this proposal is welcome as a contribution to a critical national debate and as a demonstration that a new airport is feasible and deliverable."
But Campaign to Protect Rural England (CPRE) spokesman Jamie Weir said: "Many South East airports such as Manston currently have plenty of runway capacity, so why are new airport proposals being pitched on a daily basis?
"The question of whether we actually need fresh capacity is the one which needs to be answered before we start looking for sites. This proposal, like all of those in the Thames Estuary, fails to even recognise this.
"We believe that the UK government must prove the need for additional capacity before anything like this is contemplated."
The government has asked a commission headed by Sir Howard Davies to advise on future UK airport capacity needs, with a full report due in the summer of 2015 - after the next general election.
Existing proposals for increased airport capacity in the South East have included the expansion of Gatwick and Heathrow and more use of regional airports.
There have also been three different plans to build airports in the Thames Estuary - a floating airport designed by architects Gensier, another plan known as Boris Island after it was backed by London mayor Boris Johnson, and proposals for a hub airport on the Isle of Grain designed by architect Norman Foster.
Willie Walsh, chief of International Airlines Group, which incorporates British Airways, has previously said the cost of building a hub airport off Kent would have to be recouped from charges, deterring operators from moving there.