The third runway at Heathrow could be built ABOVE the M25, the Transport Secretary has suggested.

Having approved the new runway to expand air capacity in the South East, Chris Grayling says a ramp could be built over the motorway, roughly to where junction 14 of the motorway is at the moment.

The government has been forced to think outside the box about where to build it because of the airport's location at the junction of the M25 and M4.

A view from above Slough, looking eastwards at the airport. You can see the runway extending over the M25 just south of the junction with the M4

The runway will be long enough to cope with the new generation of super-large aircraft such as the Airbus A380 and Boeing 747-8, and planes will take off directly above the M25, making for an interesting spectacle.

Remarkably this sort of runway 'ramp' above a road has been done before, in Sydney, Paris and Atlanta.

The traffic below on the M25 will be segregated according to direction of travel to create smoother traffic flow on the motorways and less weaving of vehicles between lanes.

The third runway will also be accompanied by a new terminal, taking the total to five, following the decomissioning of Terminal 1 earlier last year.

Heathrow and West London traffic will be segregated from those travelling westwards towards Slough and those continuing on the M25

The plan was made in collaboration with the Highways Agency and public feedback, but has yet to be given final approval.

A vote on the Heathrow expansion will be held in Parliament in Winter 2017/18. If plans are approved, it is unlikely that construction will be completed before 2025.

Heathrow hopes that half of its users will use public transport to get to and from the airport by 2030.