A man and a woman have died and 10 passengers are seriously ill after a coach crashed near Heathrow Airport.
Fire crews had to cut passengers from the wreckage
The London-to-Aberdeen National Express coach overturned, at 2345 GMT on Wednesday, on a slip road from the M4 to the M25 in west London.
At least three of those hurt are children and some of the people taken to hospital have lost limbs.
National Express said it was likely many of the 65 passengers were returning from holiday.
Sixteen ambulances, four rapid response cars, a number of doctors, three patient transport vehicles and an equipment support vehicle from the London Ambulance Service attended the scene.
National Express helpline: 0121 625 1278
Police witness appeal: 0845 8 505 505
Brake Support line: 0845 6038570
Firefighters used hydraulic cutting gear, airbags and thermal imaging cameras to help rescue seven people, and five were released before they got there.
The injured were taken to a number of hospitals, the majority to Hillingdon Hospital, including the man and woman who were confirmed dead.
A spokesman for the west London hospital said 38 passengers were taken there. Of those, two are still in a serious condition.
He added another patient was a 14-year-old boy and one person had undergone an arm amputation.
A further 16 casualties were taken to Charing Cross Hospital. One of those was later transferred to another hospital, and three are "giving doctors cause for concern", a spokesman said.
The coach has now been moved from the scene
Seven of the injured, including a one-year-old and a two-year-old, were taken to West Middlesex Hospital in Isleworth, west London. A man and a woman are described as being in critical conditions.
It is believed a child has been admitted to St Mary's Hospital, London, and another to Wexham Park in Slough, Berkshire.
Four of the casualties are being treated at St Peter's Hospital in Chertsey, Surrey, and the condition of all of them is described as "serious".
The coach was a No 592 service which departed London Victoria at 2230 GMT and was due to arrive in Aberdeen at 1030 GMT.
As well as the passengers two staff were on board the service, which was due to stop at Heathrow Airport, Carlisle, Hamilton, Glasgow and Dundee.
Police said they did not believe any other vehicle was involved in the crash but investigations were continuing.
The coach has been loaded on to the back of a lorry and has now been moved.
The crash closed the slip road from junction 4B of the M4 leading to junction 15 of the M25 clockwise, where the accident happened. It has now reopened.
National Express chief executive Paul Bunting said the coach was one of a pair but the other was not involved in the crash and continued its journey.
He added most of the passengers were going to Glasgow.
"It's quite likely there were holidaymakers, and certainly some foreign nationals, on board as well when the coach left Heathrow," he said.
"We know we had some Polish nationals as well as Scottish people."