A police sergeant faces the sack after being caught on CCTV injuring a woman by pushing her into a cell, it emerged today.

Sgt Mark Andrews is shown dragging Pamela Somerville, 59, across the floor of the police station in Wiltshire before shoving her into a cell.

CCTV footage captured her lying on the floor for a minute before struggling to get up with blood pouring from a head wound.

Former soldier Sgt Andrews, 37, was eventually convicted of assault causing actual bodily harm after a trial at Oxford Magistrates Court earlier this summer. He will be sentenced on Tuesday and is expected to lose his job.

The case was brought after another officer at Melksham station reported his behaviour to a supervisor.

It happened in July 2008, when Ms Somerville was arrested after being found asleep in her car. She was detained for failing to provide a sample for a breath test.

Then aged 57, she was thrown in the cell at Melksham police station after being grabbed in the station lobby by custody sergeant Andrews.

CCTV footage shows Andrews coming back into the cell after she gets to her feet and calls for help before another person comes to check her and paramedics are called.

She was taken to Royal United Hospital in Bath and needed stitches in a gash above her eye.

Ms Somerville told the Mail on Sunday: "I still find it hard to watch the images of me staggering to my feet with blood pouring from a head wound because I can remember how terrified I was.

"I could have died.

"It seems utterly barbaric that an innocent person can be treated in such a horrific and violent way and then left alone, the fact that someone may even have been watching the CCTV footage of me not moving on the floor."

Andrews was suspended on full pay after his conviction.

In a statement, Wiltshire Police's assistant chief constable Patrick Geenty said: "We are very concerned when anyone is injured in our custody and the court has decided that this injury was as a result of a criminal assault by Sgt Mark Andrews, a member of Wiltshire Police who was performing duty as a custody sergeant at the time.

"We respect the decision of the court and the force has formally apologised to the injured lady for the assault she suffered while in our care.

"People have a right to expect that the police will always act by placing the safety and welfare of the public as their first priority. This is particularly so when in police custody when irrespective of the reason for their detention, people should feel and be safe."

He said 16,000 people a year were dealt with in Wiltshire custody centres in what could be a hostile environment, adding: "Despite the rigour and effectiveness of our systems and training, it will never be possible to provide a 100% assurance that our guidelines, on occasions, will not be broken.

"Whilst that is unpalatable, the reality is that policing is complex and difficult and again we repeat, there can never be any excuse for excessive behaviour by police officers or police staff."