I was always going to act, literally ever since I was tiny. In fact, I have Doctor Who to thank for that. I wanted to become an actor after being obsessed with Tom Baker, the fourth Doctor Who, in the 1970s. His was the definitive performance of all time in anything.

I still am a geek, I don't think there's anything wrong with it. I see no shame in having an unhealthy obsession with something.

It's very hard to be objective about something you're in, especially when you set it up against things that you experienced as a child.

I'm a good person, I hope. But I'm never as good as I want to be, never as nice as I want to be, never as generous as I want to be.

Getting the call to be in The Goblet of Fire was like being welcomed into the most exclusive upper circle of some elite actors' club. You sit on set with the cream of the National Theatre and the RSC, all clutching wands or wearing witches' hats.

I mean, you know, while I'm acting on stage I'm ranking quite high, but in a room with Barack Obama I'm probably into negative digits. I never feel very famous.

We seem to spend a lot of our time in very small spaces spouting a lot of dialogue very quickly.