The exact cause of a horrific motorway crash in which a Rickmansworth woman was killed will never be known, a coroner has said.

Divya Shah, 47, died on the afternoon of March 15 this year when the Land Rover Freelander she was travelling in veered off the M1 and into a tree.

Mrs Shah, formerly of The Drive, was travelling back from an engagement party in Leicester with her husband and son when the accident happened between junctions six and five.

Hatfield Coroners Court heard this morning how the vehicle, driven by Mrs Shah’s husband, veered suddenly across the carriageway, over a grass embankment and into a tree.

Mrs Shah, who was sitting without a seatbelt in the back seat, died at the scene.

Witnesses travelling in front and behind the vehicle explained how it had been driven at a constant, safe speed before the accident. Road conditions, they added, had been perfect.

Two police experts also confirmed there was nothing mechanically wrong with the vehicle. Its brakes and tyres, they said, were “in good working order”.

Investigating officer PC Louise Rayner also confirmed that Mr Shah had not been drinking and had not been using a mobile phone at the time. His diabetes, she added, did not appear to be a contributing factor to the crash.

Vehicle expert PC Ian Marsh added: “There are various causes that could have contributed to this accident but we can discount most of them. The only one that we can’t discount is illness or that Mr Shah fell asleep.”

Coroner Graham Danbury, passing a verdict of accidental death, concluded: “Despite everybody’s best efforts we still do not know what happened here, but that is not uncommon.

“We regularly deal with cases when a vehicle driven by a fit and alert driver leaves the road in this way.

“It only takes something very minor for a vehicle to be put on an irreversible route to disaster.

“Nothing that the investigators have been able to turn up has been able to give an answer but something went wrong here. Something went wrong for a moment or two.

“We are left with something happening in the vehicle which made it take this course. But, clearly this was accidental.”