Ewan McGregor is annoyed with the British film industry, and isn’t afraid to say so. "We’ve lost the plot in Britain," he says in the press notes to Young Adam: "If we keep churning out cheesy romantic comedies about people getting married, audiences will get bored. They make whole movies dedicated to people desperate to get married. Who cares? I don’t know these people. Who are they?" And, just to make sure he knows which movies he’s referring to, he adds "And where do they live? Notting Hill, I suppose."

It might seem ungrateful for an actor with such a charmed career to be complaining. After all, he wasn’t even out of drama school before he was cast in Dennis Potter’s Lipstick On Your Collar (1993), and before he knew where he was he was made a local hero and eventually an international star by a succession of movies from Shallow Grave (1994) to Moulin Rouge (2001) and this month’s Down With Love (2003), working along the way with everyone from Peter Greenaway to Todd Haynes to Ridley Scott to Tim Burton. All this and Obi Wan Kenobi too. What has he got to complain about?

But a quick look over his CV reveals that his only British successes have been with Danny Boyle – one of the very few British directors able to make distinctively British and commercially successful films – on Shallow Grave, Trainspotting [1996], and A Life Less Ordinary [1997]. Otherwise, nothing of any significance. And it is hard to fault his analysis: this year, the only British movies likely to compete with their American counterparts are Calendar Girls, a female The Full Monty (saggy old people stripping for dignity), and Love Actually, Richard Curtis’s directorial debut.

This would be acceptable, if not encouraging, if we were making small-scale parochial films that were finding a dedicated if limited audience, as in many European countries, but this isn’t happening either. It is evidently this niche to which Young Adam aspires, and by saying "It’s important that we make films like Young Adam," McGregor might seem to be inviting critical blowback. Can it possibly live up to this kind of pressure?

Remarkably, it fully justifies McGregor’s confidence. Based on the book by legendary bohemian Beat scumbag, sell-out and heroin proselytiser Alexander Trocchi, it is possibly best described as inaugurating the genre of ‘canal noir’. Elliptically skipping back and forth in time, it follows the meanderings of Joe (McGregor), once an aspiring writer but now working on a canalboat alongside Les (Peter Mullan) and his wife Ella (Tilda Swinton). A corpse fished out of the canal by Joe and Les precipitates a shift in their relationships; but does Joe, sexually rampant but paralysed with ennui, know more about it than he’s letting on?

Young Adam has attracted much comment because of its sex scenes, but these are striking less for their explicitness (which is moderate, although we are granted another viewing of Little Ewan) but their tone, which is cold and sometimes disturbing. In particular, in the scene towards the end between Joe and his ex-girlfriend Cathie (Emily Mortimer) in which he humiliates her and covers her with food, the question of how consensual or mutually enjoyable the experience is remains unresolved.

These scenes are not about sex, but about Joe’s alienation and lack of feeling – for those around him, or for anything much. Writer-director David Mackenzie has a sure touch and has an extraordinary grasp of the expressive power of cinema, his images operating in counterpoint to the taciturn central characters. He is clearly a filmmaker to watch. McGregor, meanwhile, has never been better, finally shaking that youthful air of play-acting that has dogged him through his best projects. Swinton and Mullan are without doubt two of Britain’s best actors, and invest Ella and Les with humanity without prettifying, and Mortimer confirms her growing stature. Some will chafe at a film unafraid to leave its characters opaque and unsympathetic (even Joe’s weak attempts to do the right thing amount to little), but McGregor is right to break out the champagne. One masterpiece is no substitute for a healthy film industry, but Young Adam is a mature, impressive film, and for that we can all be grateful.