THEY'RE locking the cell doors and throwing away the keys at HMS Larkhall Prison as Bad Girls bows out with a Christmas special. Prisoners and officers have served their time - eight years' hard labour on ITV1.

The timing is right. The series has been struggling of late to come up with plots as outrageous as those that won the series viewers' awards, big ratings and a cult following.

I'll be sorry to say farewell to Bodybag, the two Julies, the Costa Cons and other inmates and officers, but it really is time to close the gates of Larkhall for good.

These Bad Girls were conceived on a train journey - a delayed one that gave TV executives Brian Park, Ann McManus and Eileen Gallagher time to formulate a show they originally called Jailbirds.

Park and McManus had Coronation Street connections - he was its producer, she was a script executive - and Gallagher was MD of LWT. Corrie writer Maureen Chadwick became the fourth member of the team that set up independent production company Shed, which went on to give us the even more outrageous (and also axed) Footballers' Wives.

I seem to recall that the makers always insisted Bad Girls was real, based on research and inmates' stories. The mad plotlines and over-the-top characters made you doubt this at times.

Forbidden love (between the governor and a prisoner), nasty prison practices like declutching (don't ask, I can't tell you in a family newspaper but it's nothing to do with driving a car) and the presence of male officers, thanks to equal opportunities legislation, all played their part in the early years.

The first episode was transmitted on May 8, 1998, only to be met by hostility from critics and indifference from viewers. It took a few episodes for the series to establish a house style and steadily build up its audience. Now the show is a cult with dozens of websites devoted to Larkhall, and a massive fan club.

The reason it's been finding the going hard of late must be attributed in part to the disappearance of many of the characters we know and love - or hate in the case of Prison Officer Jim Fenner (Jack Ellis), a pantomime villain of a bad guy whose behaviour was often worse than any crime committed by the prisoners.

Alarmingly, Ellis said that Fenner wasn't just a product of the writers' imagination. "I know there are officers like Jim Fenner out there. Not many, but they are there," he said.

This was a screw who took his job title seriously, getting intimate with female prisoners at every opportunity. Notably, he shared a cell bunk with Shell Dockley, a woman who made Lucretia Borgia look like a canteen tea lady.

"Evil personified" was one of the nicer things said about Shell (played by Debra Stephenson, now better known as Corrie's Frankie Baldwin). Stabbing Fenner with a broken bottle was one of the nicer things she did inside.

She was jailed for the kidnap, torture and eventual murder of a woman who "stole" her boyfriend. Other original Larkhall inmates represented a variety of heinous crimes, including arson (Denny Blood), prostitution (the two Julies), killing people by spiking oysters in a restaurant (Shaz), mercy killing (Barbara) and murdering the policeman who tried to rape her girlfriened (Nikki Wade). Whatever happened to good old-fashioned shoplifting?

One thing was for sure, Bad Girls was completely unlike previous prison dramas such as Within These Walls and even the ludicrous Aussie import, Prisoner: Cell Block H.

One character who has survived to the end is Sylvia Hollamby (Helen Fraser), the prison officer affectionately known to inmates as Bodybag. Her speciality is moaning and badmouthing everyone. As someone once put it: "She does an excellent job of keeping any kindness in check and the spirit of Thatcherism alive."

We can, perhaps, judge Bodybag from some of her utterances. "My Bobby's doing his braised meatballs tonight. I've been slavering all day," tells you a lot about a woman. She always thinks the worst, refusing to believe prisoners can turn over a new leaf and go straight. As in: "She's got more chance of coming off the nasty than I have to being invited up to Cliff Richard's hotel room for cream cakes and sex."

She ends the series as acting governor of G-Wing being visited by ex-inmate Natalie Buxton as a sort of Ghost of Christmas Past, come to take Bodybag on a very strange journey into the murky world of Bad Girls.

There could still be life in these Bad Girls. A rollicking musical version was premiered at West Yorkshire Playhouse in Leeds earlier this year to good reviews and enthusiastic audiences. If it gets a transfer to the West End, these Bad Girls could make good on the London stage.

Bad Girls Christmas Special is on ITV1 on Wednesday at 9pm.