Green goddess

Tamsin Greig is talking in a quick, breathless manner about the wonders of chance encounters. As she does so, her eyes grow wide as if to convey the excitement she feels about them, and her eyebrows climb her forehead. At one point, she mentions icebergs, but in a purely metaphorical sense, I think. It's hard to keep up.

"When you are on the telly, it is an occupational hazard that people will go,'You're off the telly, aren't you?'," she begins, a slice of wholemeal toast halfway between plate and mouth." And that's basically the entire exchange. Mostly, but not always. I had this really nice chat, this most wonderful chat actually, with a guy on the tube the other day. I'd tripped over his feet, as I do, and he was embarrassed and I was embarrassed and then he couldn't stop looking at me. I didn't know if it was because he wanted to shout at me for stepping on his feet or because he thought he recognised me. Eventually, he asked me if I was me and I told him yes, and we had this really wonderful conversation about why he was on the tube, why he is retiring and what it means to be at that age to have both parents and grandchildren. And this was on the tube!" Here, the eyes become huge, and the eyebrows are all but lost to her hairline. "That's brilliant, isn't it? To sit on something like the tube and have such an intense conversation for three stations ... Well, I think it's incredible."

The toast, finally, reaches her mouth, and she takes a tiny bite.

"And that, as far as I'm concerned, is the only good thing about recognition. It brings people together." Now she frowns. "But I'm not suggesting that I, personally, am responsible for creating beautiful, cataclysmic reactions among the general public - of course I'm not. But I do like to think that being recognisable can help spark the kind of conversations strangers otherwise wouldn't have. The thing about people is that we are just so close, you know? People, all the time - so very close."

Here come the icebergs.

"I watched this fantastic documentary about icebergs the other night. It was fascinating. Basically, an iceberg is this mass of potential energy, a block of giant possibility, and yet all it does, mostly, is melt. If it cracks or turns over, or if a ship runs into it, it can explode and cause all kinds of havoc, but if it doesn't, then nothing happens at all. And sometimes I think that's what it's like to be alive, you know? Tube journeys are just carriages of potential waiting to happen, and most of the time, nothing does. And that's a shame."

She pauses, wrinkles up her nose and seems suddenly to take notice of our surroundings. It's 9.30am on a damp Wednesday and we're seated in a caf alongside a gaggle of young mums and laptop- bearing young men having breakfast. The cappuccino machine is roaring, a baby is crying, and toast is being busily buttered.

"Sorry," she says, now self-conscious. "Am I talking a right load of old bollocks here?"

She thinks perhaps she is, and endeavours to explain why. She doesn't do many interviews because, as an actress, "it's my job to be other people - I feel weird being myself in front of you". Sometimes, she says, she can go off on tangents and doesn't know how to find her way back again, even when she has something to plug, like now. We are here to talk ostensibly about some Shakespeare she is doing in Stratford-upon-Avon, but this charmingly wayward woman won't quite stay on topic. She asks me as many questions as I do her, and at one point warns me not to misquote her - "I remember everything I say"- and begs me not to be a "bastard" when I come to write this up. She picks up her toast but changes her mind, and puts it back down again.

"So, what do you want to know?" she asks, with mock seriousness. "Because I don't really do much. Basically, my job is to look surprised on the telly. That's all. It's no great talent, if you really stop and think about it."

For the past few weeks now, Tamsin Greig has been looking exquisitely surprised on the telly because Green Wing has returned to Channel 4 for its triumphant second series. Green Wing remains the most deliciously surreal programme on the box, a warped comedy set among the corridors of a hospital in which patients are nothing but a minor aside in the dysfunctional lives of its erratic, certifiable staff. Among the weirdos and wackos is Greig's character, Doctor Caroline Todd, a comparative oasis of kooky calm amid the chaos.

"I suppose you have to see the world through somebody's eyes in the show," she reasons, "and that's what Caroline Todd is there for."

Greig's character is the kind of woman who is hapless at work and hopeless in love, all teeth and bed hair, and with her blouse tucked unwittingly into her knickers. If there is a door in front of her, she will walk into it. She is, I tell the actress, absolutely adorable.

"Really?" she says. "But she's annoying, too, right? She's a right pain in the arse."

Green Wing has been a deservedly big hit with audiences and (most) critics. Last year, Greig picked up a Royal Television Society award for her performance, as well as a Bafta nomination for Best Actress. But its success has also prompted an awful lot of flak.