Police have said that more than three months after the M5 crash which claimed seven lives and left 51 injured, they are still trying to establish why the tragedy happened and whether it could have been avoided.

The 34-vehicle crash on the northbound carriageway of the M5 near junction 25 at Taunton, Somerset, was the worst motorway accident to hit Britain’s roads for a decade.

There were no bad weather warning signs on the M5 on the night, November 4 last year, despite the fact that the Met Office had told the Highways Agency of: “isolated fog” in the area on the day of the crash.

Police are also investigating whether smoke from a nearby fireworks display may have contributed to the pile-up. Some motorists reported smoke or thick banks of fog causing vision problems.

An Avon & Somerset Police spokesman said: “All possible contributory factors to the fatal collision are being fully investigated, including environmental factors, weather conditions, driver behaviour, vehicle condition and distraction.

“The investigation aims to establish what occurred that evening, identify if it could have been foreseen/avoided and what can be done in the future to prevent incidents of a similar nature occurring nationwide.

“This process involves a number of agencies including the local authority and department of transport.

“In the fullness of time, the investigation findings will be made public.”

A BBC investigation last December revealed that transport chiefs were advised to upgrade fog warning systems 18 months before the crash. The site was known by authorities to be a highly fog-prone stretch of motorway.

A report to the Highways Agency had recommended installing an automatic warning system triggered by fog. The report said it would be “cost-effective” and easy to build because much of the required infrastructure was already in place.

Automated systems are already used on the M25 and the technology has been installed on a number of motorways in the North West.

The current system on the M5 is manually activated if fog is seen on the ro ad – either via CCTV or from police calling in to the Highways Agency control centre. Tonia White, from Taunton, lost her parents, Tony and Pamela Adams, of Newport, South Wales, in the crash.

The couple were on their way home after visiting their daughter.

The other victims were: Malcolm Beacham, 46, of Woolavington, near Bridgwater; Terence Brice, 55 of Patchway, Bristol; Kye Thomas, 38, of Gunnislake, Cornwall; Michael Barton, 67, from Windsor and Mr Barton’s daughter, Valerie, 30.

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