I had a feeling that my “best movie of the year” comment in last week’s Little Miss Sunshine review would come back to bite me on the ass – but I didn’t expect it to happen quite so quickly.

Adapting from a novel by P. D. James, Cuarón’s savage hand-grenade of a film takes current social ills to horribly logical conclusions. The world of 2027 is at once overwhelmed by overpopulation and crippled by a plague of infertility, so that life is a worthless commodity and birth a barely-conceivable miracle. The government herds immigrants into thinly-veiled concentration camps, yet the death of the world’s youngest person at the age of eighteen is cause for national mourning. Poised on the brink of civil war, the only question seems to be whether mankind can exterminate itself before it dies of old age.

Our window into the maelstrom is Theo, played by a surprisingly on form Clive Owen. Once a social activist, Theo has abandoned himself to despair and concordance with the status quo, until a former girlfriend (Julianne Moore) draws him back in with a simple request: acquire travel papers for a young immigrant girl who is trying to flee the country. But things rapidly spiral out of control, and Theo soon finds himself caught up in events that may determine the fate of the entire human race.

Owen plays the deadpan everyman part very well, while Claire-Hope Ashitey is convincing as his unwilling charge. But Children is a quest narrative at heart, a film constantly in motion, and so most of the other characters are resigned to cameos. Of these, Michael Caine shines as Theo’s hippy revolutionary friend, bringing humour and pathos to a world largely devoid of either. The rest of the supporting cast are somewhat thinly drawn, and in some cases, little more than caricatures.

In another film that might be a crippling fault; in Children of Men it’s almost a virtue. There’s simply too much going on, too much to think about, to get hung up on every minor character. In any case, this isn’t an actors’ film – from beginning to end, it belongs to Alfonso Cuarón. Considering that he only really came to notice with 2001′s surprise independent hit Y tu mamá también, and that he’s probably more famous as the director of the third Harry Potter film, his direction is an absolute revelation. His filmmaking here is bravura, the kind of leisurely self-assured brilliance that you might have expected from Kubrick on a good day.

And yet, what astounds most, it isn’t showy at all. Granted, it looks radiant, thanks to cinematographer and previous Cuarón collaborator, Emmanuel Lubezki, whose shifts of visual tone keep pace perfectly with the director’s vision and infuse life and texture into even the most drab surroundings.

But, there’s no flashy editing, there are no shots that serve no purpose but to draw attention to themselves. Instead, there are moments like the one a third of the way in, when our protagonists drive into an ambush and escape in reverse whilst under constant attack: at first it’s merely exhilarating and elaborately choreographed, until you realise that Cuarón has shot the entire sequence, all five minutes or so, in a single unedited take. And then, just in case anyone might think it was a fluke, he does the same thing again towards the end … only more so.

Although people are drawing comparisons with the similar and recent V for Vendetta, I think the fairest point of reference here is seventies near-classics like Soylent Green – the kind of bleak, intelligent, dystopian sci-fi that nobody seems to want to make anymore. Children of Men is thought-provoking, even downright scary if you’re open to its message; but it’s also thoroughly exciting, more so than the average Hollywood explosion-fest because there are real characters and ideas behind the action. Ultimately, it’s a long time since anyone has made a science-fiction film so bleak and incendiary, so well-realised – or for that matter, so damn good.