They all come home in the end. Like Gary Oldman for the excoriating Nil By Mouth, Tim Roth has forsaken Hollywood's bright lights for his own first venture behind the camera. And that's not the only thing he and Oldman have in common: The War Zone, like Mouth, plunges wholesale into the dark heart of British life, with hardman Ray Winstone on hand to seal the deal.

He is the antique dealing husband of Tilda Swinton (neither is named) and father of two teenage children, Tom (Freddie Cunliffe) and Jessie (Lara Belmont). They've recently moved down from London to a ramshackle cottage on the Devon coast, and Mum's just given birth to a new baby daughter. Life isn't easy, especially for the mopey, crater-faced Tom, but they are muddling through. They are happy.

Until Tom arrives home unexpectedly one day to find Dad and Sis sharing a bath. He has inadvertently stumbled across the family's dirtiest laundry, and the more he prods the more uncomfortable that knowledge becomes: Dad has been systematically abusing his daughter for years.

Roth has ordered a number a changes from Alexander Stuart's original novel, not the least of which is exchanging lazy summer days for the rain-lashed depths of winter. It's a dark film, as much physically as emotionally. The sun never shines, the cottage has lights burning day and night and no one ever smiles very much. (Didn't they even bring a TV with them?) If the novel is hermetic, then the film is oppressive. The cast is equally trimmed, with few faces visible outside of the family. Roth looks to drama when the film is at its quietist: when everything explodes, as it must, it's at its most ordinary.

And yet his major gamble, even while he pumps up the agony and racks down the illumination, is to make The War Zone beautiful. It's a stark one to be sure, hewn of dark rocks and seething seas, but beauty all the same. Roth has spoken of Bergman and Tarkovsky - classic non-Hollywood cinema - and it's that latter, in films like The Sacrifice and Stalker, that informs Roth's eye. Paradoxically, what cries out for the obvious boxed-off TV frame is opened up, given space in the luminous 'Scope photography. This is a film of contrasts: of the claustrophobia and raging seascapes; of happy families and the rubbed raw horrors beneath. It's a game mirrored in Simon Boswell's elegant score.

Winston is as good here as in his stellar turn for Oldman, playing the devoted family man who is as much in denial of his nature as he is a demon. Quiet and insidious. The two youngsters, making their debuts, are equally as good. Stuart's screenplay is unsparing and Roth has chosen well, particularly in Belmont, whose low-key playing implies - but never condones - an unsettling complicity. Swinton, though, has maybe the hardest job of all. She is never protagonist, never involved and, therefore, essentially reactive. She holds the centre while the others rage. The film would be considerably diminished by her absence.

It's not without flaws. Roth's vision is so hard, so dark that you can only wonder at how this family ever got as far as it did. Closing in the season undoubtedly focuses attentions, but it makes the film an even more gruelling experience that you might expect. And, likewise, a brief, sexually ambiguous interlude in London simply obscures matters and unnecessarily breaks Roth's spell. Sensibly he jettisons the book's bizarre, surreal coda, preferring that the piece end rather than resolve. And thank God it's only 90 odd minutes long, for, like those other exemplars of bleak, The Terence Davies Trilogy and Kieslowski's A Short Film About Killing, it's an emotional endurance test everyone should take but that few will want to repeat.