His two older sons, Joseph, 15, and Isaac, nine, who were sitting in the back, pleaded with their father not to allow David to steer.

The divorced industrial cleaner, who had been drinking but was not over the legal limit, was killed when the vehicle hit an object between junctions 12 and 11A, left the carriageway and hit a tree.

Mr Mourier died of head injuries, while his three sons escaped with only minor injuries.

Joseph told an inquest in Gloucester that his father had asked the seven-year-old: "Do you want to help change lanes?"

He told police that he had argued with his father, telling him he could crash or kill someone, but Mr Mourier had insisted he was in control and told his son "not to be stupid".

The inquest heard that Mr Mourier often allowed his son to sit on his lap and "drive" the car.

David had been steering the Rover while his father rested his hands on the top of the wheel when the crash happened on March 4.

In recording a verdict of accidental death, Gloucester coroner Alan Crickmore said Mr Mourier had been "excessively foolish" and exonerated his son of any blame in the accident.