Romola Garai is perfect as Jane Austen’s Emma

Her attitude today is resolutely un-neurotic. Unfortunately, we live in a society that's entirely body dysmorphic, and our perception of the way people should look is based on the photographic image. We all look at each other and ourselves and think we're too fat. It's become a mass cultural lunacy. And like anyone, I'm subject to the same madness. I never diet, but I exercise. A couple of times a week I will throw myself round the park. I never enjoy it, but I do it.

I think about food as something that's joyful and not just something that fuels me. I know there are people who look at a plate and divide it into calories and that's' Depressing? Yes, but also, you know, I'm lucky. There's no way you can have this conversation and ignore the fact that genetics come into it. I'm very lucky.'

She loves the Anchor & Hope gastropub on The Cut; last night she cooked kedgeree for her sister, her brother-in-law and their child, which they ate off their knees in front of Come Dine With Me. For her birthday party this summer, she cooked poussin, chocolate brownies, and complex Ottolenghi salads with samphire and lemon. I kept asking if people liked them but they were all too drunk.'

She is just as down-to-earth about her charity work. Talk to most actors about their UN mission and you get a torrent of worthiness, but Romola is more circumspect about her recent trip with the UN Refugee Agency UNHCR to the Al-Tanf refugee camp on the Syrian-Iraqi border. It was a camp of about 600 people, and there hadn't been much attention drawn to that particular camp.' She made a short film about it for The Guardian online. I didn't pretend to know everything about it, I'm just an actor.' But a small film like that can make a difference?

I don't know. I'm not convinced it does, actually. I'm not convinced it's not just an exercise in making me feel better. It's a really divisive issue among actors. If I said that to a lot of people I know, they would get up and storm off Some people I know and have worked with and count as friends believe very deeply that because they have a public profile, they should use it for good. The thing I struggle with, on a personal level, is that it's never going to be enough to make a difference. The fact that people are reading the articles to look at the celebrities seems to be the problem. It's not a good way to tap into people's altruism; it's not going to convince people to live more simple lives or distribute their wealth.'

Would she ever go into politics? She has friends who work for the Lib Dems, so if she had a sympathy it would probably lie in that direction, but she has no plans to get involved. Why not? Because I don't want to live a public life, outside of my work.' She wants to keep her family life and her romantic life off limits. And you can't have it both ways. You can't say, "I want to be a private person, apart from my political beliefs and my handbag line." Perhaps I should start a handbag line, by the way, and call it Rom-Sac.'

She often tries to defuse situations using her wit, and this happens when we talk about the dark experience of filming Glorious 39. It's a very unsettling portrait of an adopted daughter's alienation from her step-siblings, who torment her. Garai has revealed in the past, before she developed her personal privacy policy, that she has an elder brother and sister, Ralph and Rosie, who are both adopted and who are black, and a younger genetic sister, Roxy. The analogies between the film and her personal situation are striking. Yes, it was very personal to me for those reasons. I had two adopted siblings. We treated them just the same way, of course.'

While making Glorious 39, though, she did get the chance to meet her long-term heroine, Julie Christie. I was so excited and desperate to talk to her and ask her irritating questions. About the media, she was quite interesting because she said, "Don't do anything, don't do any interviews, don't lead a public life, don't relate to the outside world at all," and I thought, "Well, if you're a goddess like Julie Christie you don't have to..." '

Poliakoff, she says, is more interested in characters as cultural ciphers rather than as people. So then you have to make them into a character that people can build an emotional engagement with, and that's a process he leaves up to you, by and large, which is interesting.' Then she turns on a sixpence. Maybe it's not interesting. I dunno. It's interesting to me.'

You get the feeling it must be quite exhausting being Romola, having all that quicksilver, self-critical intelligence washing around. But essentially, she doesn't take life too seriously. Unlike a lot of actresses I know, I don't feel my work gives my life meaning. For me, it's more like play, it's something I enjoy, and if I didn't do it for my job I would do it as am dram.'

Her mobile rings. It's Stephen Poliakoff. I always get really excited when he calls. I think he's ringing because we're going to the Toronto Film Festival together for Glorious 39. Stephen has a pathological fear of flying, and has been having lots of hypnosis so that he can fly, and he said would it be all right if we all travel together, with his wife and Bill [Nighy] in one big group, so that there are people he can talk to, but I feel just a little concerned because
11 hours is a long time. What if we run out of conversation? "Stephen, I've brought Cosmo, we can do the sex quiz" '

Romola Garai doesn't particularly care if you like her or not. Perhaps that's part of what makes her so intensely likeable. And seriously, I don't think she need worry about running out of conversation.

Emma is on BBC One next month