Yelling can be heard as two police officers bundle a drunken yob, kicking and screaming into a cell.

Elsewhere in the custody suite a terrified student or professional who has never been arrested before sits wondering if they are about to get a criminal record that could wreck an otherwise promising future.

Enter volunteers like retired bank manager Frank Peirson, 63, from Abingdon, or Peter Cackett, 75, from Banbury. They are custody visitors who give up their time to check on the welfare of people held in police cells.

The visitors meet up outside a police station to walk in unannounced.

Volunteers are asked to carry out a minimum of six visits a year, making sure detainees are being treated in accordance with the Police and Criminal Evidence Act 1984.

Mr Cackett said: "Usually detainees are quite happy to see us. Sometimes they are a bit worst for drink or drugs, but by and large it is okay.

"When you see them they can be very confused and worried and you can have a chat with them and put them at their ease."

Mr Cackett said the worst part of the role is seeing youths. He said: "It irks me as a father that they get into that situation at such a young age."

Mr Peirson said there are two sort of people who end up in police cells.

He said: "It can be someone's first, and last, time in custody, and they are frightened of the publicity of the justice system and what their boss might say.

"Then there are the regular villains and they see you because they are bored rigid.

"You can tell the regulars. The first time I ever went in there was a 15-year-old girl in with her mum and a family solicitor."

There are about 16 things a custody sergeant must do when they check someone into the cells. Mr Peirson said: "The telephone never stopped ringing and the custody sergeant missed two.

"At 15 this girl knew the system well enough to notice he had missed those two things out of 16 and pointed them out to him."

Custody visitors have to be tough but say occasionally they are emotionally affected.

Mr Peirson said: "I was there one Sunday morning and a woman was brought in in a confused and dangerous mental condition.

"I didn't see her because I was advised not to. She had been picked up at 1am, hardly dressed, and brought into the cells for her own protection.

"She was in her early 20s and for the rest of her life will never be out of the company of at least two adult females."

After their tour of the cells and the police station, the two custody visitors sit down together and write a report.

Scheme administrator Sue Seaman said: "They don't just look at the cells but will check the food preparation area, making sure food is in date and there is an adequate supply to meet all cultural needs, check the working conditions of toilets and showers and make sure the panic alarms are working.

"They check the exercise yard to make sure it is clean and that the working environment is safe for custody staff as well as detainees."