Boris Johnson has ditched his idea of an island airport in the Thames Estuary in favour of one on the Isle of Grain.

In an interview with The Sunday Times, the London Mayor said the Grain scheme proposed by architect Lord Foster would “knock the spots off” rival airports on the continent and make Britain the “global capital of aviation”.

It offers the “greatest single potential for regeneration and economic growth”, he said.

Mr Johnson, who has long pushed for an estuary airport, is due to submit his thoughts and ideas to the Airports Commission this week.

It was set up by the government last year to solve the thorny issue of what to do about the country’s aviation capacity.

In his submission Mr Johnson will say the four runway airport would open in 2029 and handle 90m passengers, the paper claimed.

The first stage would cost £20bn, which he believes could be financed from private investors.

Expanding the road and rail network would add another £20 billion and increasing passenger numbers to 180 million would cost a further £10 billion.

Prime Minister David Cameron is “open to the idea” of a Thames Estuary airport, he insisted.

Lord Foster’s firm Foster and Partners are due to formally submit their plan on Friday.

The Thames Hub would have four runways, handle around 100 million passengers a year and operate 24 hours a day.

The Airports Commission is headed by the economist Sir Howard Davies.

An interim report from the commission is set to be released in December.

A final document containing recommendations for the government is due to be published in 2015.