The Prisoners, BBC One

“The best times I've ever had were in prison,” says Crystal, aged 23, one of the three inmates being followed in The Prisoners (this was originally planned as episode one, but was bounced from the schedules by the death of Baroness Thatcher). On the brink of being released after serving a 12-week stint for drink-related crimes, she's waxing nostalgic, while her girlfriend Toni – also due out very soon – is in tears. “I'm dreadin' getting out,” she quavers.

We also get to meet Jayde, 18, a prolific offender prone to self-harm, and Emma, 23, a well-spoken middle-class girl whose drug habit has seen her living on the streets. All three are inmates of HMP Holloway, one of the largest women's prisons in Europe. Over the course of a year, we watch them serving time, then being sent back into the world – and then, in one case, being remanded back into custody almost straight away.

Like Crystal, Jayde (pictured right with Buster) is fond of Holloway, seeing its staff and inmates as an extended family. “I do love prison and I do miss it, but sometimes you've got to try and move on,” she muses wistfully. Estranged from her mother, who has been in and out of jail her whole life, she's living alone in a grotty flat. However, she only lasts two weeks before she's back behind bars again. She greets the warders like old pals.

Eager to live with her girlfriend and make her family proud, Crystal seems more likely to cope, but her homesickness for the safe, secure routine of the prison ward is palpable. “I learnt to read and write in Holloway,” she declares, leafing through various certificates of merit. “Everything I've ever achieved has been in prison.” Despite her best intentions, it all goes wrong for her too, in the most dramatic and harrowing of ways.

There are a few tiny rays of hope (as when the prison staff introduce Jayde to the therapeutic value of tidying up), but they're soon obliterated by the cold water of reality. This is a depressing story where the outside world is a scarier place than the inside of a jail cell, and it's full of bleak ironies and skewed mindsets. “I do worry about Jayde when she's not in prison,” one kind-hearted prison officer remarks.

Meanwhile Emma, who takes up with her druggy boyfriend on the outside, proudly announces that he is going on a Methadone script. “We can take time off,” he explains smugly. “Emma doesn't have to go out shoplifting.” The last we hear, she seems to have vanished.

Producer/director Louise Malkinson and her team show enormous tact in capturing scenes that probably no one involved would want witnessed, and on occasion it's like visiting the far side of the moon, it's all so topsy-turvy. There's no comfort – least of all, perhaps, in the glowing endorsement that the prison service receives from Jayde and Crystal. For all the manifest skill and saintly patience of Holloway's staff, you can't help reflecting that the less prison-like prisons become, the more confusing it is for the inmates. Or maybe it's just that everyone else needs to be more caring?