James McAvoy has revealed that large amounts of Scotch helped him get into character for his new film Filth.
The Scottish actor joined co-stars including Eddie Marsan, Joanne Froggatt and Imogen Poots, director Jon S Baird and writer Irvine Welsh in London's Leicester Square for the premiere of the dark comedy.
Based on Welsh's novel of the same name, McAvoy stars as Bruce Robertson, a corrupt policeman who is competing with his colleagues for a promotion when he is put in charge of a murder investigation.
McAvoy revealed he drank whisky at the end of each day to try to forget his dark and disturbed character.
He confessed: "I drank a hell of a lot of whisky and that helped me get out of character. But in the morning, I had such a headache that it helped me get into character, so that was good."
And the actor insisted the film did not glamorise criminality, but confronted mental illness.
He said: "No matter how horrible Bruce gets, or how abusive he gets or how bigoted he gets, we know he's sick.
"We're not condoning his behaviour, we're condemning it actually, the film condemns him. But we're still asking you to feel something for him, because he's a human being."
Downton Abbey star Froggatt plays love interest Mary.
She confessed: "It was scary. Jon said to me the character could either be English or Scottish, and I said 'I'd like to play Scottish'. And he said 'Let's go for it, and if it's not good enough I'll tell you and we'll just play her English'.
"So on the first day of rehearsal with Jon and James I was terrified and I kept saying 'Oh my God, I'm so sorry guys, I'm just going to hit you with my Scottish accent, and see what happens. If it's awful, just tell me'.
"And there was a little bit more work to be done, but it was enough to pass Jon's vigilant ear, so he let me do it, which was great."
Filth is already out in cinemas in Scotland and is released in the rest of the UK on Friday.