One man was killed and three were seriously injured in the crash

The man who died was one of four people travelling in a white van which came off the carriageway, over the crash barrier and ploughed into a concrete bridge support.

Another man was airlifted to hospital in a critical condition, and two others are seriously hurt.

All three westbound carriageways of the motorway were closed between junctions 16 and 17 near Chippenham, Wiltshire, after the crash at 1430 BST.

10-mile tailbacks

The road was shut for four hours while police officers investigated the scene, causing 10-mile long tailbacks.

Two people travelling in another car involved in the accident were not seriously hurt.

Inspector Wayne Smith, of Wiltshire Police, said: "Unfortunately, when we get a fatality we have to compile a report for the coroner.

"I'm sure the family of the person who died will want to know what happened and we only have one chance to capture evidence, be that skidmarks, marks on the road, or on the vehicles.

"That means it is necessary to close the road to safely conduct the investigation."