James McAvoy at Filth premiere

James McAvoy at Filth premiere

James McAvoy admits he found it difficult filming some sex scenes for his new movie 'Filth'.

The Scottish star plays corrupt police officer Bruce Robertson in John S. Baird's big screen adaptation of Irvine Welsh's twisted novel of the same name, and while he wasn't fazed by his misogynistic, drug-taking character's scheming behaviour, some of the riskier scenes proved a challenge.

Speaking at the London premiere of 'Filth' in Leicester Square last night (30.09.13), McAvoy told BANG Showbiz: "I wasn't disturbed by anything. Except there was a scene where I had to pretend to force a 15-year-old girl to do something sexual ... and that was absolutely harrowing to do. The actress wasn't 15, she was 21, but that was really, really horrible."

The 34-year-old actor underwent a complete make-under to portray the unhealthy middle-aged policeman as he descends into madness - a challenge he relished as he is always drawn to dark characters.

Quizzed about what draws him to disturbing roles, McAvoy said: "The opportunity to make people look at a side of themselves that they wouldn't normally examine and cast some light on it and entertain them by making them do that."

Despite his character's abhorrent nature, McAvoy wanted to give him some humanity in his desperation.

He explained: "There's nothing redeemable. The film condemns his actions quite clearly. However, we do ask you to feel some kind of empathy for him, some sadness. To wonder what it might be like to be in his shoes."

Best-selling author Welsh and leading ladies Imogen Poots and Joanne Froggatt joined McAvoy on the special blue carpet at the premiere.