Filth

This is another film adaptation of an Irvine Welsh novel that was referred to as "unfilmable", although when reading the book when it first came out I for one was struck by the tightness of the narrative and the cinema-friendly focus on a single protagonist.

The antihero in question is Bruce Robertson (James McAvoy), a dodgy copper trying to make the most of a promotion opportunity by ruining his rivals through a series of cruel intricate schemes. Meanwhile, his mind is deteriorating, and he's haunted by flashbacks, waking dreams, and humanoid livestock. The film is fairly faithful to the source, and the changes (including some understandably blunted edges) are down to the different artform.

Irvine Welsh has said that McAvoy's performance is better than De Niro's in Taxi Driver. I don't think this is a suitable comparison. Scorsese's seminal feature was about a post-traumatic depression, whereas Jon S. Baird's film is more manic. For me, the film Filth most resembles is A Clockwork Orange. Like Kubrick's masterpiece, the entire aesthetic is informed by the subjectivity of the central character. And there are subtler nods: the use of classical music, the bleached windows, Jim Broadbent's reinvention of the Deltoid character (a probation officer then, a psychiatrist now), and the visual reference to 2001: A Space Odyssey.

Before the film's release, I wasn't convinced by the casting of McAvoy, but after watching it I can safely say he's transformative – to capture such bipolar savagery and the fear in a single facial expression is the sign of a special performance. The supporting cast provides a colourful blend of caricatures. Jamie Bell, Eddie Marsan and Imogen Poots all make an impact in the few moments when McAvoy isn't dominating the screen.

For me, the dud notes concern the tone of the film. Sometimes Baird's shifts between the schizoid black comedy of Robertson's outbursts and his introspective guilt about his past are so sudden and sentimental that their capacity to convince is lost in the (lack of) transition. Part of this is down to Clint Mansell's disappointingly soft score, whose tinkly piano and lifeless strings often feel incongruous, more awkward than deliberate.

But these minor issues don't detract from a powerful, funny, and finally moving depiction of mental disintegration. To say that it's the best Welsh adaptation since Trainspotting may not be saying much – so I'll say instead that it's a very good film in its own right.

Mister Tumnus, I've a feeling we're not in Narnia any more…

Think you know James McAvoy? Think again. His performance in Jon S. Baird's adaptation of Irving Welsh's Filth is astounding and there is nothing sweet or fluffy about it or any other aspect of the film. Filth is very funny, very wrong, very sordid and very likely to incite hatred from Daily Mail readers across the land. Sex, drugs, more sex, more drugs, violence, corruption, depravity, even more sex and drugs… Filth is absolutely, well, filthy, and is a memorable experience to say the least.

My companion for the screening, Bag, made two comments that stood out post-screening. The first I agree with entirely: "With the thousands of films I've seen over the years, this is the first one I've come out of wishing that I'd made it." The second, that it was a film to appreciate rather than enjoy, I'm going dispute. Call me debauched, immoral and twisted, but I enjoyed every last nanosecond of Filth.

But that's not to say it is always easy viewing. Far from it. Sometime after the midway point the laughs die down, the stomach churns a little more uneasily, the grimaces are more evident and the intakes of breath are more audible. We are less willing to forgive but, like the car crash up ahead that has caused all the drivers in front to rubber-neck, well, just one long look as we pass can't hurt, can it?

Bruce Robertson (McAvoy) is a bigot. He's bi-polar, a junkie, sex-obsessed, self-obsessed, manipulative and frequently thoroughly unpleasant. He's also a cop. With a promotion in the balance, Bruce is up against several colleagues and sets about turning one against the other, unsettling them with salacious gossip and blatant lies to ensure he beats them to the post. Throw in his manipulation of fellow freemason Bladesey (Eddie Marsan), his sultry wife, Carole (Shauna MacDonald) and his hallucinatory sessions with Doctor Rossi (Jim Broadbent) and you have one monumentally screwed up anti-hero. And what's not to love about that?

The Cohen brothers may have the monopoly on fantastic character names, but nobody writes actual characters like Welsh and the cast that Baird has poured into Filth is staggeringly good in their interpretation of this mess of freaks and misfits. There isn't a poor performance in the entire film from the uncertain laddishness of Ray (Jamie Bell) to the fantastic absurdity of Doctor Rossi. While none are bona fide Hollywood stars, the cast that glitters in a maniacal, dirty way is a treat beyond expectation: Imogen Poots, Shirley Henderson, Gary Lewis (yes, Billy Elliott and his dad are reunited at last!), John Sessions, Joanne Froggatt…

Filth is a perfectly paced film; it roars ahead stirring emotions and judgment, exciting and thrilling as it trashes everything in its wake but it is never so fast that we feel left behind or that we've missed out on a juicy morsel of degeneracy. Sufficient time is allowed for us to filter through, as best we can, the quagmire that is Bruce's life, but Baird never pauses or permits us time to glance at our watch or neighbour.

The soundtrack, too, is bang on the money stamping though a musical landscape that is at times acceptably cheesy and more often a reminder of what to check is on the iPod. Where else can you effortlessly segue from David Soul into Shaking' Stevens? While the latter is consigned to audio wallpaper, the bizarrely fantastic cameo from David Soul is a delight. Had Dennis Potter snorted cocaine Pennies From Heaven might have resembled this.

Yes, there are elements of Welsh's novel that are missing (no police dogs here…) from Filth but there always have to be excisions for film adaptations and there's no reason, in this instance at least, to mark down a film for that. No, Filth is superb and as near to perfect as I've seen for many months (since Broken and Trance).

If the trailer excited you, take the plunge. If you're a nun, a granny, my mother, or lack a strong stomach and nurture your prudishness, take a very long, very fast walk in the direction of something much safer. Dixon of Dock Green this ain't!

If you look in the mirror and see something slightly off-kilter grinning back, however…

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Inside the mind of a sex & drug addict policeman. His addictions are so deeply rooted in his personhood that they have entirely taken over his life and are the driving force in everything he does or does not do. Addiction means there's never enough and in his case drugs or sex.

This could have easily been a docudrama, instead it is a crime/comedy with a bit of drama. McAvoy is simply superb as the central mad hero and we undergo with a him a binging trip in corruption and debauchery where everyone in his life become objects he comes to use for his own gratification.

Despite the comic element being the one that has the most gravity, we get to see the torment that haunts addicted people and he too is a tormented man and his actions are a smokescreen of his anguish with his refusal to get hep only adding to his misery.

Quirky, fast paced and fun this is one heck of a mind trip.

Funny and dramatic at the same time. The main character of the film causes double feelings. On the one hand, he is disgusting and pathetic, but on the other hand, he is lonely and seriously ill. Guilt eats away from the inside of the protagonist. This can be seen from the last phrase: "The rules are the same everywhere." Everyone pays for their actions...

Probably my favourite film of 2013 so far. Gripping all the way through, with all the aspects you need from a feature length film. Yes, it has the obvious overtone of 'filth', but it's not at all in its nature... it's humorous and very touching at times. I think the casting is brilliant and I have a new found respect for James McAvoy, who in previous films I have found to be almost nondescript. He shines here, brighter than most Oscar winning performers I've seen. Ray Donovan's Eddie Marson is also fantastic in his role, so well cast - he's funny and warm in such a subtle way. This is not one of those situations when someone can rightly say 'the book is better' - I think the job has been done so well of adapting it into film format that the book is not better at all, just a different experience. It is honestly a film I want to see again. I think an instant classic, not filthy at all, but pure class.