Victim's mother says PC should be kicked out of the force after conviction for pulling her son from a car and headbutting him

The mother of a 14-year-old boy who was headbutted and assaulted by a Metropolitan police constable said the officer should be kicked out of the force for attacking a child.

The woman, who cannot be named to protect her son's identity, told the Guardian that during the assault of her teenage son, her nine-year-old was screaming: "Mum, come and get us. Please help us, Mum."

She spoke out after PC Keith Bartlett, 43, of the Territorial Support Group, was convicted at Westminster magistrates court on Friday of assaulting the boy. Two other Territorial Support Group officers were acquitted of assault.

The woman, who lives in Middlesex, said her sons and another relative were on their way back from a classic car show in Park Royal when they were stopped by police in a van.

Her elder son and the driver of the car, Lee Rosier, 24, were pulled from the car and attacked. The 14-year-old boy was thrown onto the car and headbutted by Bartlett, the court heard.

The boy's mother said: "That officer should not be in the police. He has attacked a child. I brought my children up to respect the police, to teach them right from wrong, and it's not right he is still in the force."

She said when her son came home his lip was bleeding and he had a lump on his head from where he had been struck by the officer's head.

"I thought he had been in a fight," she said. "When he said it was the police that had done it I just screamed. I couldn't believe it."

Bartlett was one of three officers from the Met's Territorial Support Group charged with assault in connection with the incident near Hanger Lane, west London, on 1 March last year. Rosier, who admitted he had been using his mobile phone while driving, and the teenage boy, who cannot be named as a result of a court order, were forcibly removed from the vehicle, assaulted and left with cut lips.

Bartlett was convicted after a four-day trial. PC Colin Nye, 38, was acquitted of assaulting the boy, and PC Anthony Read was cleared of assaulting Rosier.

The nine-year-old, who witnessed the assault, gave evidence in court.

The police claimed that they smelt cannabis when the car doors were opened but asked if they had searched the car, they said no.

Bartlett will be sentenced on 2 April.

The Independent Police Complaints Commission (IPCC) mounted an inquiry after the victims complained about their treatment. The watchdog passed a file to the Crown Prosecution Service, which decided to prosecute.

The IPCC has also submitted a report to the Met's directorate of professional standards.

Scotland Yard said the officers were still serving but had been placed on restricted duties. A spokesman said misconduct proceedings would now be considered against them.

Mike Franklin, an IPCC commissioner, said: "After a full trial, the judge decided that PC Bartlett's actions towards his victim were criminal in nature. This young man had committed no offence and offered no resistance when officers stopped the vehicle he was travelling in. We do not expect our police officers to abuse their power and positions and, as this case shows, when they do so in this way they will be held accountable by the courts."