As the makers of costume drama know, there is something very watchable about squalor, vice and poverty when you’re safely distanced from it by a couple of centuries. But if viewers to the final episode of ITV’s Moll Flanders had nipped over to BBC2, they would have been given a disconcerting reminder that, for some women, life in today’s Britain can seem as grim as it was for Moll.

In the tradition of Cathy Come Home, King Girl is a play with an overt and unequivocal message: the troubled and troublesome teenagers who wreak havoc in school and on the streets are in dire need, not of a short, sharp shock, but some serious TLC. This Grange Hill for grown-ups, as uncompromisingly harrowing as anything in Cracker, is about two 14-year-old classmates in a northern comprehensive who have both lost their fathers.

Gail is grief-stricken because hers has recently died. Glenn’s, on the other hand, has slung his hook. When he does visit, it’s only to remind Glenn that he’d always wished she’d been born a boy, to slap her face, and beat up her mother. She’s the mum from hell. When she’s not on the booze, or on the game, she’s on a hospital trolley having her stomach pumped after her latest suicide attempt.

When she deigns to talk to her daughter, her language is as brutal as everything else in her life. Unloved, and full of self-loathing, it’s no surprise that Glenn seeks her revenge through bullying.

Nor is it a surprise that she chooses Gail as her victim. She’s the ankle-socks, teacher’s-pet, butter-wouldn’t-melt type. The death of her father has left her emotionally vulnerable and a sitting target for Glenn’s sustained programme of intimidation, and viciousness.

It would be comforting to think that this is mere sensationalism - that premeditated evil on this scale couldn’t really happen in a school playground. But there have been enough headlines over the past couple of years to suggest that writer Philomena McDonagh is simply telling it the way it is.

It would be easier, too, if Ms McDonagh had allowed the audience the luxury of focusing their sense of outrage on Glenn. But however much we hate the sin, we are compelled to sympathise with a sinner whose salvation would probably require nothing more miraculous than a few cuddles.

The point is hammered home by an unashamedly schematic script, and underlined by Louise Atkins’ mesmerising performance as Glenn. When she spies on a couple making love, it isn’t prurient interest we see in her eyes but a longing for someone’s arms to cradle her. When she goes on the game, it’s not really for the money but to find if there is someone in the world who might actually want her.

Unlike most plays with a school setting, King Girl doesn’t reduce teachers to caricatures. This only serves to emphasise how ineffectual they can be when it comes to dealing with the bullies and the bullied. Of course, the problem isn’t one that schools can tackle without society being prepared to do something about the under-lying causes - as Glenn’s plight makes abundantly clear.