Hugely controversial plans for a £40bn off-shore airport in the Thames estuary could still take off, the Mayor of London said today.

In a move likely to be greeted with dismay in Kent and Medway, Boris Johnson raised the stakes in the long-running debate.

He said the option must be considered if London and the south east is to meet the rising demand for more aviation capacity.

At a meeting this morning, Boris Johnson said: "For London to retain its position as the heartbeat of global business we need aviation links that will allow us to compete with our rivals.

"No other city even approaches the volume of passengers handled at London's airports.

"But we need to start planning for a brand new airport that can help meet the ever increasing demand for aviation and act as a hub to the rest of the UK."

He confirmed that the Thames Estuary would be considered among a range of locations for the new airport.

Mr Johnson, who is risking being put on a collision course with not just council chiefs but his own government, will publish a report which makes the economic case for a new hub airport in the south east.

The latest twist over in the saga of what has been dubbed Boris Island came at a seminar at City Hall, the Mayor’s HQ.

Mr Johnson appeared alongside Daniel Moylan, the deputy chairman of Transport for London to outline how best to meet the demand for more capacity - including an off-shore option in Kent.

The Mayor’s continuing support for the idea comes despite Prime Minister David Cameron all but ruling it out late last year.

He said there were no plans for an airport in Kent, Medway or the Thames Estuary.

Medway Council moved swiftly to condemn today’s attempt to breathe new life into the much-criticised scheme.

It also revealed Transport for London chiefs tried to persuade the authority to back the scheme by suggesting new roads and train lines were built in Essex.

Rodney Chambers, the leader of Medway Council, said he was boycotting the event in protest.

He said: "It is time the Mayor of London, Boris Johnson, realises his pie in the sky Thames Estuary airport plan will never get off the ground.

"It has already been rejected by the government and the aviation industry – with nine out of ten air carriers saying they oppose the scheme."

He went on: "Despite this, the mayor seems intent on carrying on regardless, wasting public money to try and get support for his project.

"This morning he is doing this again, holding a seminar to discuss the need for increased aviation capacity and a new hub airport for London and the south east."

"I was invited to this seminar, but decided not to go, although I have already informed Daniel Moylan, the deputy chair of Transport for London, of our view when he was dispatched to my office by the mayor to try and cut a deal over their airport plan."

That deal involved a pledge that Kent would be spared the impact of new roads and other infrastructure by building it all in Essex, said Mr Chambers.