James McAvoy proud of his Filth performance

James McAvoy, with Irvine Welsh in the background, in Edinburgh today for the world premiere of Filth. Picture: Phil Wilkinson

The Glasgow-born actor, visiting the capital for the world premiere of Filth, believes his performance as a sexist, racist, misogynistic, homophobic detective is “right up there” with his iconic role in Atonement alongside Keira Knightley.

But the 34-year-old - whose performance his likely to shock many of his fans - admitted he was wary about taking on a big-screen version of Irvine Welsh’s controversial book because of the way other adaptations of his work since Trainspotting had been handled.

It has taken Welsh and director Jon S Baird around five years to bring the project to the cinema after their first discussions - at book launch hosted by the author on a boat in London. Welsh, in Edinburgh for the film’s world premiere at the Omni Centre last night, said the pair were almost “performing somersaults” after McAvoy slipped into the role to try to impress them during an initial meeting to discuss the film.

McAvoy said: “When I heard it (the original book) was by Irvine I wasn’t certain about it all. The other movies that have been made recently never really translated as well.

“I love his work and I just thought: ‘I don’t want to **** it up.’ I read the script and thought that although I wasn’t obvious casting for it, I instantly knew how to play the character.

“I’ve rarely closed a script when I’ve known exactly what I want to do. I got back to my agent right away to say I was interested.

“It’s inspiring to have so many ideas in your head on the first reading and to think: ‘thank christ there’s something out there that’s really bold and brave and not afraid about the fact it is potentially controversial or offensive.’

“It’s a virtue that it is. There’s not much out there at the moment, particularly with English speaking cinema. Everybody is hedging their bets dramatically. That doesn’t make for good drama.

“The other thing I’m really proud of is we got the film made and it exists. It’s a monument to Irvine Welsh and his amazingly particular, individual, abusively beautiful view of Edinburgh and Scotland, and also of humanity. It was something I was really proud to be part of.”

Welsh believes Filth is just as good as Trainspotting thanks to the performance of McAvoy, best known for his roles in Atonement, The Last King of Scotland and the first Chronicles of Narnia film.

The author said: “James got back to us very quickly and seemed very excited to get approached. But when he met him he seemed very young, he only looked about 15. I left him to speak to Jon to see if they bonded but when I came back he was basically in the role.

“He has morphed from a smiley wee guy to this 40-year-old divorced cop. I was blown away by this sneering, nasty guy who almost had a five o’clock shadow. He really knew the part already.

“Jon and I were literally performing somersaults and high-fiving each other after we’d met him. He blew us away. Once you have somebody like that involved everyone wants to work with him.

“When I saw the first rushes James’s acting was just so strong that I knew Filth was going to be potentially another really big cultural moment in British cinema.

“I’ve been watching Filth and Trainspotting a lot recently. They are both such strong films. Danny Boyle is one of the best visual stylists ever and the acting performances in Trainspotting are great, but the acting performances in Filth are on a different level from anything I’ve seen.”

Filth, which sees McAvoy’s wayward police officer vying for promotion while battling a string of personal demons, is the capital’s second taste of big-screen glamour in the space of a week following the European premiere of Sunshine on Leith.

But while Sunshine on Leith has been hailed one of the feel-good films of the year, the capital’s tourism leaders are unlikely to embrace Filth - described by Welsh as being like a “Greek tragedy - when its hits cinemas this weekend.

McAvoy has, however, already won widespread acclaim for his performance as Detective Sergeant Bruce Robertson, whose desperate actions at work and extra-curricular habits eventually leave him trapped in the depths of despair at the height of Edinburgh’s festive season.

McAvoy’s character is having an affair with the wife of one colleague and making sinister prank calls to his best friend’s wife.

The actor is almost unrecognisable at times as he plunges into a downward spiral of alcohol, drugs, mental health problems - and lying and plotting against his colleagues - when he is supposed to be leading a murder inquiry.

Having suffered his own marriage collapse, he is offered the chance of redemption by a recently-widowed mother, played by Downton Abbey actress Joanne Froggatt.

A string of big-named Scottish actors are in the film, including Shirley Henderson, Martin Compston, Shauna Macdonald, Kate Dickie and Gary Lewis.

Other members of the star-studded cast assembled by Baird include Jamie Bell, John Sessions, Jim Broadbent and Imogen Poots, while there are even guest cameos from David Soul and Sting’s wife Trudie.

However a cameo role filmed by Welsh, who appeared briefly in Trainspotting, as a journalist who confronts McAvoy’s character in Filth was left on the cutting room floor.

Like Sunshine on Leith, the film was shot in both Edinburgh and Glasgow, as well as Stirling, where the fictional police office was created, although some scenes were filmed overseas - in Belgium, Sweden and Hamburg, in Germany, which features in the plot when McAvoy’s character spirals off the rails.

McAvoy said fear was at the heart of his performance, which has already won widespread acclaim from critics ahead of the film’s release this weekend.

He added: “I was trying to key into who he was and why he behaves the way he behaves. It wasn’t about asking forgiveness, but trying to explain his bigoted behaviour.

“His fear is raging and his inferiority complex is raging. He has to build this facade, this fake person who is better and stronger than anyone else around him.”

Baird said he had desperately wanted to adapt Filth for the big screen as it had been his favourite book by Welsh. He bought it after being drawn to its controversial cover, which featured a pig wearing a policeman’s helmet.

The Aberdeenshire-born director told The Scotsman: “Bruce is such a complex character. He is all over the place. Hopefully the audience will have a huge range of emotions when they watch it.

“We wanted to keep an energy with the editing which was relentless and didn’t let up. We didn’t want to allow people to get too carried away with any of the comedy or get too depressed. We wanted it to be an assault on the senses.”