An airport in the Thames Estuary - dubbed Boris Island - cannot work and would destroy expansion plans at Manston, a Kent boss claims.

Speaking before the Mayor of London Boris Johnson today stepped up his call for a multi-billion pound hub off the Kent coast, Charles Buchanan, chief executive of Kent International Airport, said it would only work if Heathrow closed.

Examples in Paris, Hong Kong and Berlin showed that when a new airport opened, the old one had to shut. Mr Buchanan said that while some residents in West London might welcome closure of Heathrow, many would worry about the loss of thousands of jobs. How many would wish to move from West of London to the East. Kent alone would not be able to provide all the skills.

"Under the current way of thinking, it can't work," he said. "It would need some structural change at the three London airports - Heathrow- Gatwick and Stansted - to make it viable."

Manston is forecast to become a key regional airport over the next 20 years as the Government seeks to ease pressure on the London airports.

He added: "It wouldn't be good news for the likes of Manston, Southend or anywhere else. I don't see it happening, there's no political appetite for it. Why build something like that when you've got a 2,700-metre runway here?"

Meanwhile, Neville Gaunt, chairman of the North Kent branch of the Federation of Small Businesses, welcomed a healthy debate on the economic benefits of a hub airport, warning that the UK could lose out to overseas competition.

Kent businesses and the community would benefit from the new infrastructure and jobs a new airport would bring.