I love James McAvoy – dear little Mr Tumnus, Starter for 10, Atonement andLast King of Scotland – but I have never been an Irving Welsh fan.  I only went to see Trainspottingbecause I also love Ewan McGregor. So what on earth possessed me to go and see this?

My misgivings were fulfilled, I’m afraid. This seedy and bleak movie exudes filth from every pore, whether it’s the allusion to corrupt policing in refined Edinburgh, or the state of mind of our anti-hero Bruce, a beyond-corrupt copper or the squalor of his once-grand flat.

Bruce is on a mission to get the promotion to inspector, by foul means – fair doesn’t come into it – in order to win back his wife and child. Nothing is too depraved – be it framing his colleague for homosexuality, shagging his mate’s wife, or humiliating another by revealing his penis size at the Christmas party, all the while lurching deeper and deeper into drug-fueled bi-polar behaviour, seeing visions and hearing voices that allude to his past guilty secrets. 

Along the way he seeks to de-stabilise the only friend he has, nerdy lawyer Bladesey, brilliantly played by a geeky-looking Eddie Marsan (always the weirdo, last seen as evil husband in Tyrannosaur, and excellent he was too), by bombarding his wife with perverted phone calls, while pretending to be her knight in shining armour. Perhaps the scenes in Hamburg, where he takes Bladesey to educate him, are meant to be funny; I just found them sordid to the point of averting my eyes, as I did with Bruce’s obsessional porn-driven masturbation and the liberal amounts of vomit.

I kept looking for signs that there might be some redemption in all of this: is it a flicker of hope when Bruce tries to resuscitate a dying man and has a flirtation with his wife, Mary (Downton’s Joanne Froggatt, actually looking quite pretty out of her maid’s uniform)? Will he see the folly of his ways as he realises he has sunk to such depths that it is either terminal, or the only way is up? Will Bladesey come to the rescue?

Despite – or because of – Irvine Welsh’s renowned depravity there are some fine actors and excellent performances. I suppose one has to grudgingly admit that McAvoy, unrecognisably puffy and pockmarked from his normal gamine self, plays a blinder. I did not recognise John Sessions as the police chief – he too has inflated like a giant bull-frog; Jamie Bell remains skinny but nor would I have recognised him. 

Of course Jim Broadbent as the psycho shrink, Dr Rossi, looking more like Einstein than anything else, steals the show and thankfully pulls together some of the narrative thread, along with the anthropomorphic hallucinogenic talking tapeworm, which gets lost in the pools of sick and spunk that litter the screen. Looking at the cast list, I failed even to spot David Soul and others such as Tracy Ann Obermann, all playing bit parts. But I guess the film is so murky, it is hard to see through the pish and shite of Welsh’s filthy gloom.

PS The two stars are in recognition of the acting, not the film itself.