The Magdalene Sisters (15)

You'd better wash those men right out of your hair...

Two young girls, inmates of a draconian Catholic home, lie awake dreaming of freedom. The bedboard over them reads, "God is Just". There's little evidence of a just God ruling their lives, and the irony could have been crushing. But it's an ink-dark night, and you have to squint to make out the words: it shows how adeptly director Peter Mullan manages to skate on the right side of overstatement.

In its righteous fury, The Magdalene Sisters is the sort of film that might once have carried the tag-line "Torn from today's headlines!" – although, if its story had made the headlines in the first place, the film might never have needed to be made. Its topic is the institution of the Magdalene Asylums, run until relatively recent times by the Catholic Church. A young woman could be forcibly placed in one if she got pregnant or even, as a pre-emptive measure, if it seemed she might one day get pregnant. As the fearsome Sister Bridget explains, men stray into temptation, so it's the temptation, the women, that must be removed. These homes contained laundries where women worked unpaid all year round, sometimes for their entire lives. The system was a metaphor ruthlessly made literal: these women were meant to be scrubbing their souls clean.

Mullan's story is set in Dublin in 1964, although the closing caption reveals that the last Magdalene laundry only closed in 1996. And it's clear from the roll call of names seen in the titles that the film's three young heroines are themselves representative of some 30,000 stories. In the almost wordless opening sequence, Margaret (Anne-Marie Duff) is raped by her cousin at a wedding. We don't hear what's said under the festive din, but we assume that the black looks among the menfolk mean cousin Kevin's days are numbered. In fact, it's Margaret who's hauled off in disgrace. Rose (Dorothy Duffy) has just given birth in hospital where her icy-faced mother won't even look at the baby before it's packed off for adoption. As for Bernadette (Nora-Jane Noone, a newcomer with furious brio), she doesn't get anywhere near sex, just exchanges salty glances with the boys lingering outside her orphanage (St Attracta's!). Two little girls, fighting to brush her sump- tuous locks, wonder if it isn't a sin to be beautiful. Apparently it is: the next day, Bernadette's bed is empty. In a wonderfully unsentimental touch, the little girls don't weep for her, just greedily make off with her hairbrush.

Given the opportunities for wringing our tears, Mullan – who has a cameo as a violently punitive father – never lets himself grab sympathy for the girls too easily. His heroines aren't suffering angels, but flesh and blood, as their brutalisation by the sisters never lets us forget. The lead trio aren't even allowed to bond conventionally, to be jolly chums against the system – this isn't Malory Towers. Friendship and talk are forbidden, the inmates communicating through whispers and sly looks. While Margaret and Rose befriend the disturbed Crispina (a distressingly raw performance by Eileen Walsh), the increasingly embittered Bernadette becomes her dogged tormentor.

There's some bracingly black humour – the line about lepers is a killer – but no easy laughs to relieve the tension. When Margaret uses nettles to punish a sexually abusive priest, the broadly farcical result initially resembles one of those crowd-pleasing moments in Ken Loach's films where the bad guys get their come-uppance. Here, just as we're beginning to chuckle over the blubbery redness of the priest's mortified arse, Mullan gives us a savage payoff that leads to grimmer consequences still.

The film succeeds in showing the monstrousness of an institution, without suggesting in a facile way that its guardians are themselves monsters. At first, Sister Bridget, who rules this spiritual Colditz with a rod of iron – or rather, hair clippers, a belt and caustic sarcasm – seems the embodiment of cruelty. Played with vicious delicacy by Geraldine McEwan, she peers at her charges with a wizened little smirk and gloating gimlet eyes, cautioning them in a sing-song voice that brooks no dissent. But her malevolence gains depth: we see her giving a coy little Christmas speech and shedding a tear over Ingrid Bergman's silver-screen nun in the pious 1945 weepie The Bells of St Mary's. Yet only a moment later, as one girl gets her freedom, Sister Bridget lays on one last humiliation. Mullan even allows her a brief shot where she appears to be searching her soul – yet we know her certainty will never be shaken, just as, even if some girls escape the home, the system stays in place.

Indeed, Mullan's analysis of the system makes the film, by extension, as much about political as religious oppression. An older woman intends to snitch on Bernadette's misdemeanours, not out of malice but because she genuinely believes she's ensuring the girl's chances of going to heaven. We see how so many of these women collude in their oppression: some even come to love their prison, surely the religious equivalent of the Stockholm Syndrome. And we sense how hostile the outside world is likely to be to escapees: a weak-spirited delivery boy cheerfully buys the myth that it's all "hookers and hoors" inside the walls.

The film's visual style is downbeat, but not without a grim poetry and the odd starkly potent image, like a mirthless row of oranges arranged on the beds for Christmas. Cinematographer Nigel Willoughby has an eye for drab colours and textures: the girls' brown uniforms, the linen they handle, as washed-out as the older inmates' souls in a world of bitterly cold mornings and laundry-scalded hands. Only the occasional shot – like an extreme close-up of Bernadette's bloodied eye, with Sister Bridget's reflection peering out like her warning conscience – is too rhetorically fancy. The film doesn't need it: Mullan's engrossing, unvarnished storytelling could show the nuns a thing or two about rigour.

j.romney@independent.co.uk