A police sergeant has been fined £828 for head-butting a woman while wearing a motorcycle helmet in a "road-rage" attack.

David Sanderson was off-duty when he confronted two women in the car ahead of him at an Asda supermarket petrol station in Chandler's Ford, Hampshire, on June 6 last year.

Gaynor Byng told Worthing Magistrates' Court that the 45-year-old was concerned that the women were using a mobile phone, but she said it was being used hands-free.

She said Sanderson, of Portsmouth, began revving his motorcycle engine as he waited for the Ford Fiesta to pull away from the petrol station.

He was then seen to attempt to undertake the car before it stopped and the passenger, Donya Bryant, got out and confronted him.

Ms Byng said: "He began shouting at them, telling them they shouldn't have been on the phone. Both women told him to go and leave them alone."

She said the situation escalated as Miss Bryant, who was emotionally upset at the recent bereavement of a friend, swore at the defendant and threatened to kill him.

She continued: "Mr Sanderson, still wearing his crash helmet at that point, head-butted Miss Bryant to the forehead.

"This left a red mark the size of a 50p piece and a swollen lump."

Ms Byng said that Sanderson told another off-duty police officer who witnessed the incident: "You do not know what you saw, young man. I am police too."

Miss Bryant said in a victim impact statement read to the court: "I feel extremely let down by someone who, as a serving police officer, should have been protecting the public."

Sanderson had denied the offence of assault by beating and was found guilty following a trial last month.

He was fined £828, ordered to pay £600 court costs, £100 compensation and £82 victim surcharge.

Chairwoman of the bench Marley Isaac told him: "We are very mindful of your position in the force, your daily occupation and your previous good character and 23-year exemplary service.

"However, this does appear to be an ongoing road rage incident that began at the pumps and continued off the forecourt.

"The victim would have felt quite intimidated by your revving behind her.

"She clearly provoked you and the incident escalated significantly. It would have been better at that stage if you had identified yourself and it's disappointing you didn't behave more appropriately."

Paul Fairley, defending, said Sanderson continued to deny that he deliberately assaulted Miss Bryant and the case was set to go to the crown court for appeal.

He said the road traffic officer was fulfilling his duty of preventing the use of mobile phones at the wheel.

He said: "He is the sort of officer who would always seek to educate those who seek to drive dangerously or put themselves and others at risk."

Mr Fairley said Sanderson was still working full-time for Hampshire police, but faced dismissal from the force and had been taken off front-line duties pending the conclusion of the appeal.