I have very passionate, emotional, loving parents—which maybe helps with acting, I don’t know. My mom is a psychotherapist. She practiced at home. My dad, we say he’s an inventor. He invented an artificial respirator that’s used in accidents and emergencies. He manufactured the stuff that he invented, so he’s not sitting in a shed at the bottom of the garden or anything.

I have a sister who is two years younger than me. She’s an artist—a photographer—and she has her first exhibition in London right now, which is very exciting. And I have a stepbrother who’s in his early twenties. He’s at Christie’s right now, and he’s one of the expert catalogers in the U.K. of antiquarian books.

They’re a very loving, quite eccentric bunch. I go back to London four or five times a year. I called my mom already a couple of times today. She likes to know who I’ve been meeting. She asks, “What are you wearing?” I say, “I’m wearing a pair of jeans and a white shirt.” She likes to get a picture of things on the phone. My dad is going to come meet me at the Venice film festival because The Constant Gardener is in competition there. He’s very nervous.

Filming The Constant Gardener in Kenya was really tremendous. The physical beauty of the place is astonishing. We were living out in the bush in tents, and they had to fly in water. And then there were the people, particularly the people in Kibera, the slum that we filmed in. There was poverty on a level I have never seen before. There was no running water, no sanitation, no electricity.

It’s very shocking when you first see that, and you’re looking through your eyes and you’re seeing this poverty. But then you start to see it through their eyes, and it’s a very alive, spirited city that they’re living in. There’s song and dance. There’s little cinemas in the shantytown. There’s restaurants and so many hairdressers. It’s a very vibrant, vibrant life. The people were incredibly hospitable and curious and generous. It was just complicated, because you saw this very profound material poverty, but despite it, there was this incredible spiritual wealth.

The whole crew was very moved by the people and their spirit, but being moved doesn’t really help them. The producer, Simon Channing Williams, set this charity up so we can actually do something practical. We’re going to be building a secondary school in Loiyangalani, and we’ve already built a school in the slum, in Kibera. There are plans to bring fresh water and shower facilities.

Tessa [her character in The Constant Gardener], she’s a real-life woman of passions, of love and intellect. The way that the script is structured, she’s set up to be a certain kind of woman; you think she’s unfaithful, that she’s having an affair. It really plays with people’s expectations and the stereotypes of women.

Some scenes were very plot-based, and we had to stick with the script. But there were scenes—for instance, when I was walking in Kibera—when it was pure improvisation. I was interacting with the people, and they weren’t extras; it wasn’t a film set. It was complete verité. It was reportage. Similarly, in the love scenes with me and Ralph Fiennes, [director] Fernando [Meirelles] really allowed us to play and improvise and just create these very natural moments between a husband and wife. I love, love improvising. I’d do it all the time if I could.