The film that made an international success out of Mike Leigh begins with what I genuinely believe to be the most terrifying opening shot I have ever seen. As we hear a woman moaning in either pain or ecstasy, the handheld camera moves down a dark alley, shaking like an there's earthquake, and it stops at the single pool of light, where a man with his back to us has forced a woman against the wall, raping her. Twenty seconds have elapsed in the film.

A few cuts later, and the woman breaks free and screams that she's going to sic her brothers on the man, sending him into a panicked run. We're 40 seconds into the film. As the man runs, the first drumbeats of Andrew Dickson's percussion and string heavy score kick in, adding to what was already an exhausting level of tension. At 70 seconds, the man jumps into a car and drives away in it, over the screams of its rightful owner, who yells for her husband to rouse himself from the couch. At 85 seconds cut to a shot behind the car on the road in the late-night traffic, and the credits start to appear:

A film by Mike Leigh

David Thewlis

Lesley Sharp

Katrin Cartlidge

Naked

The rest of the credits play out in a shot from the backseat of the car, focusing on the road with the man in the driver's seat all blurry. The music continues on, driving timpani and tinkling strings playing off each other crazily, keeping us on edge as though the idea of being in car with an auto thief and rapist wasn't already unsettling. 195 seconds into the film, the scene cuts from the inside of the car at night to the outside of the car in the morning light, an edit as shockingly effective as I have ever seen. The car pulls to the side of the road. At 213 seconds the film cuts again, to the man standing in the middle of the intersection, looking around, and we finally get a good look at him: a skinny, dirty man in a long black coat with a ratty beard. In short order, we will learn that his name is Johnny (Thewlis), and he's just driven from Manchester to London to find his ex-girlfriend.

Words are not the right medium to describe the explosive momentum of this opening sequence, which all but left me gasping for breath. First impressions, they say, are lasting impressions; we've gotten one hell of a first impression of Johnny by now, and it was presented in some of the nastiest 3.5 minutes of cinema you will ever see.

Despite this, the particular and uncomfortable genius of Naked is that it isn't a protracted exercise in watching a terrible man being terrible, but that it burrows into Johnny's mind and takes him as a human being in full - we do not sympathise with him, but by the end of the film's 131 minutes, we understand him as well as it is possible to understand a cinematic character, and that is perhaps more frightening than a mere depiction of viciousness. Understanding how this is the case is a matter of understanding Mike Leigh's method, and why he is one of the most reliable narrative filmmakers now working.

Leigh never works with a script: he works with a story sketch, which he mulls over with his actors over an extended rehearsal period - 11 weeks for Naked. The dialogue spoken onscreen is largely the actors' creation, although it is not precisely "improvised," as sometimes is reported; it is the result of those weeks and weeks of rehearsing.

This could be disastrous, except that the director has managed to work with some of the finest (if not always the most celebrated) performers in the British film industry: Jim Broadbent, Timothy Spall, Imelda Staunton, Brenda Blethyn. The process doesn't work because it's a foolproof process, but because it's turned over to acting geniuses. And in Naked, Leigh shepherded David Thewlis (in their third and final collaboration) to give a performance that lays the very best work of those very great performers to shame. His work as Johnny is, to my eyes, the finest acting done by any Brit of his generation, the greatest single performance in a British movie in the two decades since Bob Hoskin's epochal turn in Neil Jordan's Mona Lisa.

In Thewlis's hands, Johnny is many things all at once: he is feverishly misogynistic, but only because he loves women and believes that this love makes him weak, so that he must behave as a monster to redeem his masculinity. He is clearly spiritual and obsessed with eschatology, petrified by what he believes to be humanity's impending destruction, but anxious that it should just happen already, because there's precious little to humanity worth saving. He despises the poverty that he uses as a crutch. He in short a ball of confused self-loathing, perhaps a cliché but one rarely if ever carried off with such combustive force. Though the kernel of this characterisation is Leigh's, it is Thewlis who brings these things into the flesh, as it were. He is unpleasant, easy to hate, maybe even evil; but he is also excessively charming and often hilarious, and it becomes unnervingly easy to see what it is about him that makes women look to him as a lover and protector even after he abuses them physically and mentally, abandons them, scorns them. It's a magnificent portrait of a bastard that one Thewlis that year's Best Actor award at Cannes, and should have propelled him to the frontlines of move stardom, if the world were just.

Given this incredible centerpiece, Leigh works magic to produce what may well be his greatest work, though it's a tough film to love or even respect: it's not so easy to process as Secrets & Lies or Vera Drake, and it's significantly more amoral than either - charges of sexism have dogged the film since the moment of its release, and it's not only easy to see why, it's somewhat hard to deny that those charges are reasonable. But reasonable is not the same as right, and it should be clear that Leigh is not attempting to lionise Johnny, but cast him as the symptom of a broken society.

"Things are awful." This is the overriding lesson of the film, which looks at the underbelly of life in post-conservative England, confronts us with everything bad, and then shows us things that are worse. It leaves no room for comfort in a noble hero, or a morally uplifting conclusion, because in Britain in 1993, or most countries at most times, those things are lies. Instead, he exposes his characters, his society, his audience, and leaves us defenseless. Naked.

Now, more than 1100 words in, is it too late to mention how much of the film is funny, occasionally very funny satire? Yes, I suppose it is. Just watch the damn thing.