Sergeant Terry Fry, 54, who was a Guildford neighbourhood team officer at the time, was in the custody suite at Guildford police station around 12.30am on  June 10, 2020 when the incident occurred.

The victim of the assault, a 15-year-old boy, had been arrested for a number of offences, including assaulting police, racially aggravated public order and arson.

He had been restrained in a body cuff, leg restraints and a spit hood on the floor in his cell, and was being extremely aggressive, violent and verbally abusive. A number of officers were in the cell at the time.

The court heard how Sgt Fry was assisting with the restraint and was shouting at the teenager and telling him to stop assaulting his colleagues.

Following a further verbal exchange, Sgt Fry got down on his right knee and placed his left knee in the boy’s chest before being pulled away by some of his colleagues.

The matter was reported by the boy’s appropriate adult, who witnessed the incident from the cell door.

Sgt Fry was interviewed under caution on September 4, 2020. He subsequently retired from Surrey Police in February and will be sentenced on September 1.

Temporary Assistant Chief Constable for Surrey Police Ali Barlow said: “Our officers join the Force to serve and protect the Surrey public from harm and whilst there are times where force has to be used in order to do so, excessive use of force, as seen in this case, is completely unacceptable.

“Sgt Fry crossed the line by assaulting a 15-year-old boy whilst he was already being restrained by officers in custody and today’s verdict will ensure that he is held accountable for his actions.

“Sgt Fry will be sentenced in September and whilst he has since retired from the Force, he will still face gross misconduct proceedings at a later date.”