Police believe a driver fell asleep before his coach careered off the M40 in Oxfordshire, hitting two parked vehicles and killing one of his passengers, an inquest heard.

Mavis Whyman, 60, of Vanner Road, Witney, died from multiple injuries on November 7, 2000, when the X70 coach from Heathrow Airport to Oxford went through a crash barrier at Tetsworth, near Thame.

Dc Nick Oliver, from Thames Valley Police traffic division at Bicester, said evidence from witnesses and information from a sleep research centre suggested that driver Anthony Souch fell asleep at the wheel.

But Mr Souch, of Kelham Hall Drive, Wheatley, has denied the allegation, saying specialists at a sleep clinic at the Churchill Hospital, in Oxford, had found no problem with his sleep patterns.

Lorry driver Martyn Gale, who was overtaken by the coach as he travelled north, told Oxford Coroner's Court he saw the coach veering off towards the hard shoulder. He said: "I saw the coach hit the rear of a recovery vehicle. It then carried on going left into the trailer of a lorry, ripping off the fuel tank.

"It just kept on going until it went through the crash barrier and down a steep embankment."

Mr Gale said he did not see the coach brake or take any action to avoid the collision.

Mrs Whyman and her sister Joyce Priestly had been returning to Oxford after a trip to Holland, where they had been visiting a penfriend.

Mrs Priestly told the inquest the journey had been uneventful until they noticed they were getting closer to the vehicle ahead of them.

She told the hearing she was sitting by the window next to her sister in one of the front two seats.

Mrs Priestly said: "I glanced over towards the driver because I was expecting him to brake, but he didn't.

"We seemed to be heading straight for the vehicle. The driver was just looking straight ahead. He didn't even slow down. We both screamed and there was a bang. I was thrown out of my seat and must have blacked out. When I woke up, I was on the floor beside the driver."

Mrs Priestly suffered a broken collar bone and ten broken ribs. Her pelvis was broken in three places and she had a broken bone in her left foot, a sprained ankle and a small broken bone in her back as a result of the accident.

Dc Oliver told the hearing: "Research, which has found people who are fatigued are drawn to amber flashing lights, the shallow angle of the suggested veering, and the fact that passengers actually spoke to the driver prior to the collision, indicate to me that the driver was falling asleep."

The inquest heard Mr Souch had returned from a holiday in Spain on Sunday and had taken Monday off work, the day before the accident.

Describing what had happened, Mr Souch said he moved to the left to avoid a lorry that had cut in front of him.

He said: "As much as I tried to turn the wheel away, I just couldn't. I just seemed to get sucked into it."

The court heard Mr Souch pleaded guilty to a charge of careless driving in June.

He received six penalty points and was fined.

Deputy coroner Dorothy Flood recorded a verdict of accidental death.

In response to the accident and the inquest, the Oxford Bus Company has announced that its Express drivers will be instructed to encourage passengers to wear seatbelts.

The company has also pledged to put seatbelt safety notices on the back of every seat by February 1.

Commercial manager Phil Clark said: "This was a terrible tragedy and we hope we have learned a lesson from it in terms of seatbelt safety.

"We will now be doing everything we can to encourage passengers to use the seatbelts provided so that nothing like this happens again," he added.