A controversial proposal for an off-shore airport in the Thames estuary near Sheppey has taken a significant step forward after London Mayor Boris Johnson confirmed a feasibility study would be carried out into his idea.

The idea for an airport - dubbed "Boris Island" - has already sparked widespread opposition across Kent with many saying it would be impossible to build and would do huge environmental damage.

But in a clear sign that the the idea is being seriously considered, the Mayor of London has announced that he has appointed the expert engineer behind a similar airport in Hong Kong to investigate the option.

Douglas Oakervee, who also chairs the Crossrail project for an east-west rail link in London, will carry out the study. He was the lead engineer who oversaw the £12billion Hong Kong airport which opened in 1998 and was built on reclaimed land.

Mr Johnson is understood to be modelling his plans on the Hong Kong scheme. In a statement from his office, he underlined his determination to explore every option.

The statement said: "The Mayor has made it clear that if there is an overriding economic, environmental, political or practical reason why the airport would not work, then he will not progress the project. But he is determined to consider all the arguments first so it can be decided once and for all whether the airport is a feasible option."

Sittingbourne and Sheppey MP Derek Wyatt (Lab) said the Mayor’s plan was a non-starter and accused him of political posturing. "It is political posturing to get the Conservatives off the hook while they oppose expansion at Heathrow. The only solution is the expansion of Stansted, Heathrow and Gatwick. The Heathrow expansion would cost £13billion; Boris’ plan would cost an estimated £50million."

Deputy mayor Kit Malthouse said: "To have such a colossal figure from the engineering world bringing his extensive skills and judgement to this unique and important project is great news."

In a related development, a new all-party group of MPs has been set up to lobby for Thames estuary airport plan. North Essex MP Bernard Jenkin, who is to chair the group, said: "It becomes clear that as constraints on the expansion of Heathrow, Gatwick and Stansted are fixed by public opinion, which does not want airport capacity so close to where people live, the proposal for a Thames estuary airport will move rapidly up the agenda as the only viable alternative, providing a real hub international airport to the east of London."