More than three-quarters of people do not believe a Thames Estuary airport is needed, an independent poll has found.

A nationwide ICM survey commissioned by Medway Council has found 76% of adults believe it is unnecessary to relocate London’s main airport off the north Kent coast.

London Mayor Boris Johnson is backing plans to build four floating runways in a £70billion project.

Dubbed Boris Island, his support for the proposal comes despite rejection by a host of politicians – including deputy prime minister Nick Clegg, who said it was a "flight of fancy" on a trip to Kent last month.

Medway Council has run a joint campaign since 2009 with Kent County Council and the RSPB against the proposed airport, which its argues is "undeliverable, unaffordable and unnecessary".

The authority commissioned ICM to question 1,000 adults across the UK about Boris Island.

The poll, which cost the council £460 by adding questions to a separate survey, found 81% of people think £70bn is too much to spend on a new airport.

Nearly nine out of 10 people agreed we should instead use the capacity already available at regional airports, including Birmingham and Manston, in Ramsgate.

Medway Council leader Cllr Rodney Chambers said: "This national survey shows that Boris Johnson is flying in the face of public opinion with his plan for an estuary airport.

"A Thames Estuary airport would blight huge parts of Kent and Medway as it would need a huge amount of infrastructure to support it and it would devastate one of Europe’s most important areas for migrating wildfowl.

"Boris needs to listen to public opinion, admit it is a pie in the sky idea and drop it for good."