I couldn't get any of the ingenue roles when younger because at 5 feet 9 inches with a deep voice I was always too... genue. My career has completely happened since I was 29.

I had the best teacher in the business. Kevin Costner was my teacher. I was acting opposite him and he was directing me. The way he directed me, for which I am eternally grateful, is he would watch the scene back on the monitor, which is sort of considered unfashionable - you're not meant to watch yourself. But he was like, "Come around. Watch this. See there, you're doing a great reaction, but you're doing it out of frame." That was exactly what I needed. I learned how to act on film from him.

I didn't know box office was a thing you could possess but I don't have it. I go up for lovely roles and people with this nebulous thing called box office get them so there isn't much I can do about that unless you know where I can get some box-office myself!

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.

That was a bizarre and unlikely event, which has misled a generation of drama students from my old drama school that dreams really do come true. I was an unemployed actor. I had been an actor for about eight years, and had worked in theater, and done a tiny bit of TV, and somehow an audition video of mine ended up on Kevin Costner's television screen, and he rang me up and invited me to fly first-class to Hollywood and be in his movie The Postman.

I'm on record as having said "I've done this amazing movie - The Sixth Sense - that no one is going to see." And then it stayed in the top 10 American films for about six months. So don't ask me. I'm the most disastrous PR and marketing predictor.

Carey Mulligan is completely self-possessed. She knows what she's doing, and again, quite like the big-hitters I was talking about, my job was just to feel and reflect back the amazing performance coming my way. If anything, I was slightly pathetically flying in her tailwind. She's an extraordinary actress.