I grew up in Deptford in south London, and at that time I used to wear toppers, loon pants and tonic suits from shops like Take 6 and Topman. I was a bit of a soul boy, but I had a very eclectic taste in music - I was into James Brown and Bowie; and I was the only kid in the neighbourhood who would also be listening to Chopin.

I got obsessed with classical music, I got obsessed with Chopin, with playing the piano.

People imagine that actors are being offered everything and you are not. So things come in and sometimes there are things that I want and can't get a meeting on, or go to a different actors.

And of course I've got kids of my own now, and they love me being in the Harry Potter films. I'm now part of a phenomenon. You become incredibly cool to your kids, and you get a young fan base. So you became the cool dad at school. You're suddenly hip.

I did have a knack for playing weirdos. There's still sort of this perception of me out there as being this crazy guy.

My big love was the Beatles. I was more into music.

And costume is so important for an actor. It absolutely helps to get into character; it's the closest thing to you, it touches you. Some actors like to go into make-up and then put their clothes on, but I like to dress first; that's my routine.