I've played lots of villains in my time and I think the reason they've been so successful is that they're not two-dimensional. They're not black and white. That's the gig.

Interestingly, this character [Doctor Nash] is probably closer to me than somebody like the evil Sir Godfrey in Robin Hood or Lord Blackwood who wants to take over the world in Sherlock Holmes. This is a character that's English, he's based in London, and so it's closer to me than a lot of stuff I've been doing recently.

I just like voicing films in general. I do a lot of documentary work and it's a short hop really to narrating a character, especially if you're on film and you're there in a visual way. It sounds obvious, but voicing an animation really focuses you on the way that you're communicating through your voice. It's a very specific ability that you need to be able to have in order to pitch it just right.

I think it serves the purpose of the film if the premise is that you're unsure of me because you've only ever really seen me play villains.

The idea of transformation - playing something I'm not - is the bit I enjoy most about acting.

It's great to have the chance to play a character before he goes to the dark side, or the yellow side if you will. Normally, you don't get that opportunity. The narrative of a movie usually demands that you are that guy from the start.

I got sent the script [ Before I Go To Sleep] as usually happens and you have a little look. I know it's a bit of a cliché, but it was absolutely a page turner. I mean, I wanted to find out what happened next.