The exact cause of a crash which killed a serving Trowbridge police officer as he was on his way to an emergency call will remain a mystery after an inquest recorded a verdict of accidental death.

The jury inquest, held at Trowbridge Town Hall on Wednesday, heard how PC Dan Cooper, 22, of Westlands Lane, Beanacre, died when his car spun off Westwood Road, near Bradford on Avon, on a left-hand bend and crashed into a tree at about 8pm on February 1.

PC Cooper, who had been with the force for two and a half years, was only working with the response team that evening because they were short-staffed.

He had been at the scene of a crash in Westwood Road, and was on his way to an emergency call in Southwick when the accident happened.

Eyewitness John Corden, an insurance broker from Bath, was travelling along Westwood Road in the opposite direction to PC Cooper.

In a statement read to the inquest, he said: “Suddenly and unexpectedly I saw a police car travel from the right ride of the bend straight across the road into trees on the left.

“My overall impression was that the car was out of control when I saw it and was travelling at a high speed.”

The car, a 1.9-litre Skoda Octavia, had spun in a clockwise direction before hitting the tree, coming to rest facing the direction it had been travelling in. PC Cooper died from severe head injuries.

PC Stephen Fair, of Wiltshire Police’s serious collision investigation team, said it was impossible to determine the speed PC Cooper was going at the time of the crash, but it was a minimum of 35 to 39mph. PC Cooper’s car hit the tree at a speed of at least 26mph.

Investigations showed there were no defects with the car and PC Cooper had no drugs or alcohol in his system.

He had completed a driving course for police response vehicles in 2009, and was regarded as a naturally gifted driver by instructors.

Giving evidence, PC Fair said: “In my opinion the accident was caused by PC Dan Cooper losing control of the vehicle as he negotiated the left-hand bend. The accident could have been caused by excessive speed for the road conditions, harsh steering, and/or harsh braking.”

PC Fair said that quantifying the exact role each of the three factors played in the crash was impossible.

Following the inquest, PC Cooper’s parents, Andrew and Heather, said: “We believe that the exact cause of Dan’s accident will always remain a mystery.

“What we do know is that Dan was doing his utmost to go to the aid of a colleague who was in serious trouble. Dan paid the ultimate price for his selfless dedication to duty.

“We are immensely proud of Dan and all that he has achieved in his short life, both as a police officer and as a young man.”

Wiltshire Police’s Chief Constable, Brian Moore, said: “The inquest has heard that a combination of circumstances were likely to have caused the police car he was driving to leave the road and although Dan was police trained, it highlights the risks that officers face on a daily basis, including attending emergency situations.”