It may be weeks before police know what caused the M5 pile-up in which seven people were killed, the Transport Secretary has said.
Justine Greening told MPs a total of 37 vehicles were involved in the Friday night horror crash that left seven dead and 51 injured.
Making a Commons statement on the tragedy, she said: "Given the large number of vehicles involved, the need to carefully look at those vehicles recovered and to talk to many of the witnesses, it may be some weeks until the investigation can conclude on any cause or causes of this incident."
Avon and Somerset Police are investigating whether the crash happened as smoke from a rugby club fireworks display drifted on to the M5, affecting drivers' visibility and concentration. Officers are conducting a criminal investigation.
Elderly couple Anthony and Pamela Adams, from Newport, south Wales, were among those killed in the smash.
Lorry driver Terry Brice, from Bristol, was also named as one of the victims, as was Malcolm Beacham, from Woolavington in Somerset.
The crash also left a young woman in a coma and her wheelchair-bound father and sister dead.
Emma Barton, believed to be 19, was said to have been travelling in a car with her boyfriend Christopher Burbull, father Michael and sister Maggie, when they were caught up in the chaos.
The seventh victim was named as Kye Thomas, 38, from Gunnislake, Cornwall.
Ms Greening told MPs: "While Avon and Somerset Police have indicated the presence of smoke on the carriageway is a significant line of inquiry, Assistant Chief Constable (Anthony) Bangham has been clear to me that, in his words to me early today, 'it is far too early to jump to conclusions on the causal factors of this incident'."