A leading Kent business figure is supporting Boris Johnson's plan for a huge round-the-clock airport off the Isle of Sheppey.

The Mayor of London is looking into the possibility of building a giant terminal on an artificial island in the Thames Estuary off Sheppey. Mr Johnson is said to want to eventually close Heathrow and turn it into a business park.

Mike Lazenby, chief executive of the Chatham-based Kent Reliance Building Society, has been a long-time supporter of a potential new airport at Cliffe or off the Kent coast.

"Heathrow has a limited capacity and sooner or later, there is going to be another airport in this country," Mr Lazenby said.

"If there’s an airport going, why can’t we have it in Kent? Kent is ideally placed. It would have a huge positive impact on the local economy. It would help businesses, property prices and be really good news for the county."

The plans are fiercely opposed by local council leaders and environmentalists, and it is feared they might also interfere with growth strategies at Kent International Airport, Manston, and London Ashford, Lydd.

But Mr Lazenby says a "not in my back yard" attitude failed to appreciate the benefits a new airport would bring.

"Everybody in business in Kent would benefit and people looking for a job in Kent would get a job. It makes total sense."

Meanwhile, Matt Clarke, chief executive of KIA, poured cold water on the idea, saying it had been around for several years.

He added: "At KIA, we have an existing airport on solid ground which we will continue to develop to meet the air transport needs of the people of Kent."

KIA owner Infratil is understood to be drawing up plans to expand passenger numbers following the collapse of EUjet some years ago and more recently Seguro Travel, the operator of holiday company Kent Escapes.

The RSPB is also opposed to the idea, as the Thames Estuary contains one of Europe’s biggest Special Protection Areas and is used by 300,000 migratory birds.

A spokesman said to build an airport there "would potentially be the single biggest piece of environmental vandalism ever perpetrated in the UK".