Joss Whedon writes beautiful drama. His sensitivity and his sense of drama and scenes are pretty exceptional. There's no one else writing like him, really, in sci-fi and TV. That's not to say there are no astonishing writers on TV. I was nervous about coming to America and playing an English person who speaks very English when all the writers are American, because it's a very particular thing to imitate, and if it's badly imitated, it sounds painfully contorted and silly. And he writes very well for English people. It was Joss Whedon who persuaded me.

I'm 5'9" and have the body of an English person that doesn't know how to diet.

The trouble with audition process is, when you're an unemployed actor, it's the only time you get to act, and it can be quite fun. If you feel in control of the material and you feel that the people are pleased to see you and are excited by you auditioning for them, it can be a really rewarding process. But it can also be a very humiliating process.

Usually the casting process is lengthy and humiliating, but in this instance, The Ghost Writer, it was just too easy. I was sitting in a rental car on an L.A. street and my cell phone rang, and it was Roman Polanski on the line. I couldn't really believe my luck. He said, "See you in Berlin." I sat staring at a palm tree, thinking how surreal that was.

From a very young age, I wanted to get up on stage whenever I went to the theatre - the actors just seemed to be having so much fun. One of my worries about theatre, in fact, is that the actors are quite often having more fun than the audience.

I was lucky, because Ewan McGregor had already been shooting with Roman Polanski for about a month before I got role. And he did a faultless impersonation of what it was going to be like. So when direction happened, it was like, "Oh yeah. That's what Ewan said was going to happen." And so it was a little bit less debilitating than it might have been.

It was fine when I was single and childless. Carrying the responsibility of screwing up your kids at the same time is huge. I remember when I got Peter Pan, and I told my mom and dad and my friends I was leaving - again, I was cast way late on - in the next two days to go to Australia for four months, and they all went "Bye! See you in four months!" But no one said "We need you," and I really knew that it was time to think about someone else for a change.