Children of Men

Children of Men
Grim but good... Clive Owen and Julianne Moore in Children of Men PR

PD James's future-nightmare novel of a world without children has been turned into an explosively violent and chillingly real movie, probably the best film in the Venice festival competition so far. It is directed by Alfonso Cuarón and brilliantly filmed in hard, flat, crisp detail by his cinematographer Emmanuel Lubezki.

The digitally realised vision of a reactionary, Orwellian Britain in 2027, with its seedy streetscapes periodically smashed by terrorist bombs, is eerily convincing, and the spectacular sequences of all-out urban warfare are electrifying and very scary.

Cuarón has sweetened the outlook of James's book a little, but that doesn't prevent an Arctic mood of fear and horror pouring out of the screen.

Clive Owen plays Theo, an ex-radical who is now an alcoholic with a drab job in a government office: a miserable guy in a miserable world. Centuries of pollution have caused humans to become infertile - the world's youngest person is all of 18 - and the realisation that the end of the line is nigh has led to a global malaise of despair and disorder.

Britain is toughing it out, clamping down on dissent and offering its citizens free suicide pills with the Shakespearian brand-name of Quietus; its relative calm and prosperity have brought waves of immigrants who are brutally herded into internment camps on the coast.

Theo is contacted by a former comrade and lover Julian (Julianne Moore) now the leader of a revolutionary underground movement demanding equal rights for refugees. She has a sensational secret: a young girl they have found called Kee (Clare-Hope Ashitey) is pregnant, and the movement wants to exploit her for their own ends. Kee is scared by their fanaticism, and Theo helps her escape.

There is something very British in this vision, simultaneously post-apocalyptic and pre-apocalyptic. It has something of both 1984 and John Wyndham's The Day of the Triffids, and it reminded me of Barry Hines's nuclear nightmare Threads and the 70s British television classic Survivors. Cuarón gets good performances out of Ashitey and Owen, the dishevelled and seedy guy who rediscovers his idealism and romanticism playing Joseph to a terrified young Mary, who, as she crisply informs him, is far from being a virgin.

There are great cameos, chiefly one from Michael Caine as an ageing hippy who grows ganja in a secret woodland hideout and hooks Theo up with a counter-cultural support network.

Peter Mullan puts in a bravura appearance as Syd, a border guard and one of Caine's weed clientele, who is able to smuggle them away from both the authorities and the terrorists. It's a smart and funny performance from the multi-talented Mullan, and it would incidentally be good to see him direct another film, as his last one, The Magdalene Sisters, won the Golden Lion here at Venice in 2002.

Apart from everything else, this is a great action film, with thrilling and nail-biting moments that are all the more gripping for taking place in a ruined future world, which looks all too plausible. Added to this is Cuarón's subtle dimension of metaphor and parable: it is humankind's spiritual sterility and vanity which has made possible their catastrophic despoiling of the planet. This is quite an achievement for Cuarón, who must surely be a contender for the big prize.

· Peter Bradshaw is the Guardian's film critic