Ummm...well, when I read the script, I knew I had to do the film. I tend to receive about 10 scripts a day and normally they're all in the bin after 2 pages - but this was really different, I was totally gripped.

When I heard that Marty Scorsese was directing the film - that clinched it for me. I'm a huge fan. I'd let him direct me in anything, even a bad period drama in which my talents are wasted and an overweight Val Kilmer plays Abraham Lincoln.

I think one of the main themes of the film is redemption. I like the fact that at the beginning of the movie I'm awake, but by the end I'm asleep. The film really tells a story.

I think the public are tired of those films where boy meets girl and they fall in love. This is different. When I meet Heidi - Christina's character - she doesn't even like me. I have to win her over with my sly wit and dramatic inevitability.

Obviously, for logistical reasons, I couldn't appear on set with Christina at the same time - the cost would have been enormous - so I had to act against a blue screen and then Christina was digitally inserted into a lot of scenes. It was a very interesting experience.

Once, I was sitting on the train, daydreaming and looking at my reflection in the window. An old man sitting next to me turned to me and said,"You think you're a character in a film or a book. You're not. You're a nobody."

I've always remembered that.