Imagine Abel Ferrara’s Bad Lieutenant with a Scottish swagger and a blistering sense of sarcasm and you just about have the measure of Filth. Easily the best film adaptation of an Irvine Welsh novel since Trainspotting, it features a terrific central performance from James McAvoy as Bruce Robertson. This manipulative, drug-fuelled, sex-crazed policeman is careering off the rails as he attempts to secure the promotion he believes will restore order to his wayward life.

The sheer energy and ferocity of McAvoy’s performance make Robertson a positively Shakespearean figure, pitched somewhere between Richard III and Iago as he plots and taunts, deceives and flatters, all the better to exploit the weaknesses and insecurities of anyone unfortunate enough to cross his path. He undermines rival Ray Lennox (Jamie Bell), inflames the jealousy of Dougie (Brian McCardie) and takes particular delight in exploiting the friendship of meek chartered accountant Bladesey (Eddie Marsan), who seems to regard Robertson with something akin to hero worship. Bladesey's wife Bunty (a hilarious Shirley Henderson) is soon subject to a series of heavy-breathing phone calls that she cannot entirely resist.

Jon S Baird’s film is set in an Edinburgh that feels more like the 1990s than the 21st century but that may all be part of the film’s demented, hallucinatory sensibility. The thin line between reality and grotesque fantasy is increasingly smeared for the monstrous, unhinged Robertson and it’s to the credit of McAvoy’s performance that we still believe in the possibility of redemption even as he sinks further and further into the mire. For all its outrageous humour and exuberant embrace of the politically incorrect, Filth is still a modern morality tale with some unexpected sentimentality lurking beneath its thick, scrofulous skin.

General release from Fri 4 Oct.

FILTH - Official International Trailer (Unrated)