An inquiry has been launched into the coach crash that claimed the life of a woman and seriously injured three other people on the M40.

The woman, who is expected to be named later today, was a passenger on the Oxford Express coach which plunged through a safety barrier and down an embankment shortly after midday yesterday.

A 39-year-old man with chest injuries and a 68-year-old woman with an injured pelvis were airlifted to the John Radcliffe Hospital, Oxford, and are in a stable condition in intensive care.

The 61-year-old coach driver, Tony Souch, from Wheatley, was taken to hospital in an ambulance with serious injuries.

Thirteen other passengers were treated at the hospital for minor injuries and released soon afterwards. Eight ambulances were called to the crash.

Emergency plans were put into operation at the John Radcliffe Hospital to deal with the casualties.

The Oxford-bound coach struck a French beer lorry and a recovery truck on the hard shoulder of the northbound carriageway near Lewknor.

The X70 coach belonged to the Oxford Bus Company and had left Terminal 4 at Heathrow Airport at 11.10am. It was due to arrive at Gloucester Green, Oxford, at 12.40pm.

The front of the coach was severely damaged and the side of the vehicle where the baggage is stored had been ripped out.

Emergency services say the death toll could have been much higher had the vehicle rolled down the 20ft drop below into a field.

Insp Malcolm Collis, leading the investigation, said: The side of the coach has been ripped out in the crash. It was precariously balanced on the embankment. One roll and it would have hit the bottom of the field and there would have been a lot more seriously injured people.

The 53-seater Volvo coach, which was bought new by the company in 1995 and is similar to the rest of the firm's 33-strong coach fleet, had recently passed two safety checks.

Jonathan Radley, marketing manager for Oxford Bus Company, said: "Obviously we are going to carry out a thorough investigation and we will also be working with the emergency services to see what happened. We don't know how the crash happened yet.

"We are very shocked. This is a horrible accident. Our thoughts go out to the driver and those on board and their families.

I have been with the company for six years and we've never had an accident like this in that time.

The driver of the coach, who has not been named, obtained his bus licence with the company in 1982 and, after leaving for a few years in the late 1980s, returned to work for it again in 1995.

Mr Radley said the driver was very experienced and had a very good record.

One lane of the motorway was still closed today while police inquiries continued.

The 13 injured included the mechanic from the recovery truck. The driver of the French lorry escaped unhurt.

The accident caused traffic chaos with tailbacks stretching for miles on the northbound carriageway of the motorway.

AA spokesman Adrian Ruck said the accident highlighted the need to improve safety and teach people to use hard shoulders properly.

The organisation, together with the RAC, produced a report earlier this year calling for a number of measures to improve hard shoulder safety, including improved rumble strips, pedestrian refuges at emergency phone boxes and better lighting.