UPDATE: Police this afternoon arrested a 49-year-old coach driver on suspicion of causing death by dangerous driving. He has been released on bail pending further enquiries.
A male passenger was killed and 40 others injured when a coach and lorry crashed in fog on a motorway on Saturday.
The man, 35, from Birmingham, a passenger in the coach, was killed and two people seriously hurt in the accident near Frankley Services on the M5 in the West Midlands.
Forty people were treated at the scene, on the southbound carriageway between junctions three and four.
Police said the death and one serious injury were from the coach, and the driver of the lorry was also in a serious condition. No children were involved.
Chief Inspector Carl Flynn, of the Central Motorway Police Group, said the coach had broken down in a "live" lane of the M5 before the accident.
Addressing a news conference at a Highways Agency control centre near the crash scene, Mr Flynn said a 999 call was made by a member of the public reporting the stranded coach about 12 minutes before the crash.
The officer told reporters: "At 6.12am a 999 call was made by a concerned member of the public about a coach having broken down on lane one of the M5 south.
"The Highways Agency did the appropriate signage on the network and dispatched their resources to the scene of the broken down coach as is normal practice.
"However, unfortunately at 6.24 hours a further call was received to say that a large goods vehicle had collided into the rear of the coach.
"Central Motorway police officers were immediately dispatched and arrived at the scene six minutes later and then assisted colleagues from the Highways Agency, the ambulance service and fire service to manage the scene."
Thirty four passengers - men and women - were on board the coach, which going from the Birmingham area to a place of work.
Both the lorry driver, who is from the south west of England, and a passenger on the coach are in a critical condition in hospital.
Mr Flynn added: "Thankfully, all other passengers have received less serious, or slight or no injuries and they are being cared for as we speak."
A dedicated team of investigators is now carrying out an inquiry into the cause of the accident and the southbound M5 is likely to remain closed until at least the end of today.
The most serious casualties were taken to Birmingham's Queen Elizabeth Hospital, while other injured victims were taken to other hospitals in Birmingham, Redditch and West Bromwich.
Martin Stott, of the Highways Agency, told the press conference that signs warning of an incident and urging drivers to slow down were put in place after the initial call saying the coach had broken down.
Fog warnings were already in place, Mr Stott said, adding: "We'd set information across the network on our display signs to say that there was fog and to slow down."
Anyone who is concerned for the welfare of a relative can contact a casualty bureau set up by West Midlands Police on 0800 0920410.