Ryanair's boss has called for new runways at Heathrow, Stansted and Gatwick, branding any plans for a new South East airport "absolutely nuts".
Michael O'Leary said a new hub in the Thames estuary would not make economic sense and agreements limiting expansion at existing sites should be scrapped.
London Mayor Boris Johnson has looked at plans to build an airport between the Essex and Kent coasts.
The government recently ruled out new runways at London's three key airports.
Mr O'Leary, who is chief executive of the budget airline, said: "I think it's absolutely nuts, there's no requirement for any new hub airport.
"London has five airports - you've got Luton, Heathrow, Gatwick, Stansted and London City - what you do need and we need urgently in the South East is more runways at those airports.
"We have long since campaigned for a second runway at Stansted, a second runway at Gatwick and a third runway at Heathrow because you have the infrastructure there."
He added: "I would tear up the agreement at Gatwick and at Heathrow and I would build a second runway at Gatwick and a third runway at Heathrow - this is the only way forward.
"Britain is losing out to Madrid, to Paris and to Frankfurt who are pushing forward more runways at their existing hub airports.
"Please, please don't waste billions and billions of pounds building another white elephant in the Romney Marshes or wherever it is."
In January Mr Johnson backed a report, overseen by Transport for London, which called for a new hub airport.
It said passenger demand for London's airports was forecast to increase from 140 million passengers a year in 2010 to 400 million passengers a year by 2050.
The report concluded that London's only hub airport was losing out to other European airports which, if sustained, could have long-term damaging effects on both the London and UK economies.
In May plans for a third runway and sixth terminal at Heathrow were scrapped when the coalition government took office.
The Department for Transport said it did not support the construction of additional runways at Heathrow, Gatwick or Stansted and was working to develop more sustainable aviation.