Rowan Joffe was on top of everything. He knew exactly how he wanted everything to be, right down to the fact when I made those telephone calls, I didn't do it afterwards in a studio. I think that's how he operates. He likes it to be as real and as clear as possible.

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.

In the film industry you never really know if all the various ingredients will come together - sometimes they do, and sometimes they don't. As an actor, you don't have much control over those things. It's a director's medium in that sense. All you can really do is minimise the risks of being involved in something that might not work and look for something that also suits you.

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.

Rowan Joffe is very specific. I mean, he wrote it as well and he has a very orderly writer's mind and the same applies to his directing.

If you think about Shakespeare, you remember Richard III and Macbeth before you remember Ferdinand, whose role is just to fall in love and be a bit of a wimp. I love the baddies. More important, though, is making the baddies somehow, weirdly, understood.

When you're making a psychological thriller, what you need to do is have an audience on shifting sand so they're never quite sure where they are.