'£20 toll to fund third Heathrow runway'

Heathrow's controversial third runway will only be built if passengers driving to the airport are charged a £20 toll, according to a Department of Transport study.

The massive cost of burying the M4 under a five- mile tunnel and extending the southern runway by a mile can only be met by levying the £20 "access charge" on each vehicle arriving at Heathrow, experts say.

Strict EU environmental curbs on nitrogen oxide emissions from car exhausts will prevent expansion unless the M4 and the access road that leads off the motorway is buried in a tunnel ventilated by anti-pollution fans.

The runway would bring an additional 50 million passengers and 175,000 flights to Heathrow each year - exposing 35,000 people to cancer-causing nitrogen oxide above EU limits by 2015. This number fell to only 16 if the runway complied with the suggested measures.

The study concluded that a £20 toll would cut Heathrow car trips by a third. But a transport department spokeswoman said the project was unlikely to go ahead.