Britain faces a period of economic stagnation unless a new international airport is built in south-east England, London Mayor Boris Johnson said on Monday.

The government has ruled out expansion of London's existing airports, but Johnson has lobbied for a new hub airport in the Thames Estuary, which has also been opposed on environmental grounds.

"There's no doubt that to do nothing will lead to economic stagnation. The government must now grasp the nettle and begin serious plans for the multi-runway solution," he said at the launch of a report on British airport capacity.

Johnson said developing the Thames Estuary airport, often referred to as Boris Island, should be viewed as a pillar in the government's plan for economic growth.

The plan, speculated to cost between 40 billion and 50 billion pounds, aims to increase flight capacity without expanding London's existing international airport hub Heathrow, owned by Ferrovial's BAA.

He said Heathrow is operating at 98 percent capacity and does not have the ability to add routes to growing markets in the Far East, resulting in foreign airlines going to rival European airports.

"As the world economy changes and global power shifts to the East, the constrictions of London's hub airport are becoming ever more apparent and ever more damaging."

"In the next 15 years, 75 million Chinese households would enter the middle classes - it is a phenomenal market," he said.

Speaking at a meeting of business leaders on Monday Prime Minister David Cameron acknowledged the possibility of a new international airport.

"We made a promise about not building a third runway at Heathrow but we have to look at aviation to work out how we can make ourselves more connected," said Cameron.