BUILDING four new runways to the west and using the existing terminals is one radical option being considered by Heathrow Airport, it has emerged.

The plan, which would involve tunnelling the M25, is one of at least 12 expansion proposals drawn up for the airport's owner, previously known as BAA.

A new four-runway airport in the home counties or one extra runway to the east and one to the west of the existing airport are among the alternatives outlined in leaked documents.

John Stewart, chairman of anti Heathrow expansion campaign group HACAN, said the plans showed the airport's bosses were worried they would not get the go-ahead for a third landing strip at the existing site.

"Nobody expected Heathrow would be looking so far afield. It must mean they don't feel at all confident of being able to win the argument about expanding the existing airport," he said.

"From confidently proposing a third runway 10 years ago, Heathrow Airport has been reduced to scrabbling around for a proposal that will look acceptable to local people."

A spokesman for Heathrow Airport said: "These are early drafts of concepts developed by consultants last year. They are not designs that have been endorsed by Heathrow Airport."

Heathrow Airport is expected to submit its final proposal to the Airports Commission, which is examining the need for extra airport capacity in the UK, by July 19.