A lorry driver is facing jail after being convicted of crushing to death a family of four when he fell asleep at the wheel of his truck.

Ian King ploughed into a queue of stationary traffic in his 30-tonne low loader, on the A34, at Bletchingdon, north of Oxford.

The truck crushed the Peugeot belonging to Malcolm and Janice Dowling. The couple and their sons, George aged 11 years and Richard aged 16 years, who were travelling home to Lichfield Staffordshire, from a family holiday in France, were killed instantly.

This afternoon, 60-year-old King was warned by a judge that he would be going to jail when he is sentenced in the New Year.

Prosecutors and police officers welcomed the unanimous verdict, reached by jurors in just two hours and 15 minutes.

King, from Leicestershire, had stood trial at Oxford Crown Court after denying four counts of causing death by dangerous driving.

He had claimed he had an undiagnosed sleeping disorder which had caused him to pass out behind the wheel of his HGV and that he had no recollection of the smash.

However, the jury did not believe him and returned guilty verdicts on all four counts.

During the trial the court was told how emergency services had been called to the scene, just before 3.30pm on July 31 last year.

One senior police officer said the scene that greeted them was the worst he had ever dealt with.

The Dowling's Peugeot 307 was underneath King's enormous lorry, which had rammed its way through two other cars at more than 40mph before crushing the family.

Another driver, Stephen Chance, spent three months immobilised in hospital after his neck was broken in the crash.

Drivers reported the specialist heavy-duty goods vehicle, which was capable of carrying loads up to 150 tons, had steamed at a constant speed into traffic.

Only one witness reported any sign of braking and even that was only for a split second, the jury heard.

King only discovered anyone had died when he was spoken to by police officers in hospital later that day.

He said: "I knew there had been a fatality but I did not know to what extent I had been personally involved."

Tony McGeorge, defending, had argued during the case that his client suffered from sleep apnoea, a respiratory condition that disrupted his normal sleep patterns.

As the condition was undiagnosed, King had no idea that he was in any danger of suddenly passing out, he maintained.

However, medical experts testified that there was no reason why the defendant would not have been aware that he was becoming sleepy.

Prosecutor John Price had argued from the very start of the four-day trial that for someone to continue driving while knowingly growing sleepier was to fall into the definition of dangerous driving.

Following the verdict, Judge David Morton Jack released the defendant on bail until January 11.

"The court's sentencing is subject to the guidance of the Court of Appeal and the Sentencing Guidelines Council and they indicate, in effect, the inevitability of a prison sentence," he said.

"It would not be fair to leave you in any real hope otherwise."

Following the case, Sgt Peter Jell of the Thames Valley Police Roads Policing Operational Command Unit, warned of the dangers of driving while tired.

He said, in a statement: "I would first like to pass on my condolences to the families of Malcolm, Janice, Richard and George.

"The past 17 months have been terrible for them waiting for this case to be concluded.

"The jury have convicted Ian David King of four counts of causing death by dangerous driving. They have listened to the evidence and concluded that Mr King should have stopped at the early signs of fatigue instead of continuing his journey which resulted in such horrendous consequences.

"One thing that this trial has highlighted is the devastating consequences of driving whilst tired or fatigued. I would urge every driver to take note of this trial and if they ever feel the need to continue driving whilst tired think of Malcolm, Janice, Richard and George Dowling and stop and take a break.

"I would also like to pay tribute to all members of the emergency services who dealt with events of Monday 31 July 2006. It was a truly horrific scene."