Boris Johnson's plans for the construction of new airport in the Thames Estuary have been described as being "dead in the water" by the Liberal Democrats' London Assembly transport spokesperson.

Caroline Pidgeon said that opposition from major airlines to the proposals, put forward by the London mayor as an alternative to a third runway at Heathrow, is the "final nail in the coffin" for the scheme. Environmental groups have already raised their concerns over the plans, which would have seen a major new airport built off the coast of Essex and Kent in the middle of the Thames Estuary.

A report drawn up by Medway Council also identified a range of issues that cast doubts over the plans, while stating that the airport would be located 60 miles (96.6km) from the capital - equivalent to moving Bristol International Airport to the other side of Cardiff, or relocating Manchester Airport to Leeds. Pidgeon said: "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 that 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."