Ewan McGregor and I said this to each other after we saw The Ghost Writer. Every time Roman Polanski did a "No, no, no!," he was right. It was really as if a sculptor was asked to sculpt the embodiment of despair - that was the attitude he would strike. But as with every sort of inspiring teacher you ever had who was strict and scary, when you get it right, the sun comes out, and it's worth it.

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.

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.

I am the worst judge of how a movie is going to do. I always have great and ambitious hopes, but none of them see the light of day.

I thought "I've coped with some crazy situations, and I can do this." But working with Roman Polanski is so different from the fashionable and accepted way of directing now.

I really needed to have something in my life, because I realized there were other things more important than my career. So I love having my children and my family.

I think it's quite lucky that I lead this lifestyle, and in fact, my career's only gotten better as I've looked older, because it ages you, the uncertainty.