It looks almost as if the car was steam-rollered - it is just awful

Crash eyewtiness

The man was taken for tests at Royal United Hospital in Bath and later held under arrest at Chippenham Police Station.

The incident on Friday shocked emergency services. The car was left unrecognisable in what police officers said was the worst accident they have ever had to deal with.

The family car was left resembling a twisted ball of metal, in which lay a children's book and a child's car seat.

None of the occupants have yet been identified due to the severity of the crash. Police said dental records may have to be used.

A photographer at the scene said: "There was hardly anything left of the VW car. The family would not have stood a chance.

The man is being held at Chippenham Police Station

"It looks almost as if the car was steam-rollered. Emergency crews here have been extremely affected by what they have seen - it is just awful."

Graham Chivers of Wiltshire Police said the lorry was heading from Bath towards Warminster and the car was heading the other way when they collided near the junction for the A350, three quarters of a mile from the Granada service station.

The road, which is the main route from Southampton to Bristol, was closed for 24 hours as investigators tended to the scene.

A traffic police officer said: "We know that the children were young as there was a child booster seat in the back. There was also a borrowed library book about a horse called Snowy.

"When you see something like that, it puts the whole thing into perspective."

The names of the victims will be released shortly.