London Mayor Boris Johnson has said his proposal for an island airport in the Thames estuary is not dead, despite the Airports Commission rejecting the idea.
Commission chairman Sir Howard Davies said the huge cost, economic disruption and environmental concerns made the proposal unviable.
The mayor called this short-sighted, but said plans to expand either Gatwick or Heathrow airports would fail.
These plans face huge opposition and no government would back them, he claimed.
The proposal for a Thames Estuary airport - dubbed Boris Island because of the mayor's strong backing - would have led to the development of a four-runway airport on the Isle of Grain.
: "We are not persuaded that a very large airport in the Thames estuary is the right answer to London's and the UK's connectivity needs.
"While we recognise the need for a hub airport, we believe this should be a part of an effective system of competing airports to meet the needs of a widely spread and diverse market like London's.