LEADING airline bosses have joined the mounting opposition against Boris Johnson’s proposal to build an airport in the Thames Estuary.

The proposed £40bn project dubbed Boris Island is seen by the London Mayor as an alternative to having a third runway at Heathrow.

After drawing criticism from local councils and wildlife groups, the Board of Airline Representatives UK, which represents more than 90 airlines including British Airways, Air France and Virgin Atlantic, has announced it will not support the scheme.

The board rejects Mr Johnson’s idea on the grounds of bird strike hazards and resulting unemployment at Heathrow.

Caroline Pidgeon, the Liberal Democrat London Assembly transport spokesperson, said: “This must be the final nail in the coffin of Boris Johnson’s ridiculous proposals for an airport in the Thames Estuary.

“Boris Johnson has managed to create the most incredible coalition opposed to this airport stretching from David Cameron and the world's leading airlines right through to all the political parties in Kent and environmental groups such as the RSPB.

“It is time he listened to the voices of all sensible people on this issue and just admitted once and for all that the Thames Estuary Airport is dead in the water.”

Leading civil engineer Douglas Oakervee, who found building an airport on the site was technically feasible, was due to brief the London Assembly next Thursday (March 11) on the environmental impact of building the airport.

However he has had to cancel because of business in Hong Kong and there are currently no plans to reschedule.

Dartford Council, Medway Council and Kent County Council oppose plans to build the airport as well as the RSPB.

HACAN ClearSkies, a campaign group against a third runway at Heathrow, has said building an airport in the Thames Estuary would mean low-flying planes above north Kent on a regular basis.