"I've arranged for you to have lunch with Natalie," the record company press officer says with a slight air of anxiety. "I'm hoping to find a convenient vegetarian restaurant. Obviously, it's got to be very vegetarian." Obviously. For Natalie Merchant, who has recently announced her departure as the lead singer of 10,000 Maniacs, is widely thought of as a serious young woman. She writes songs about poverty and pollution and illiteracy. She has long hair and wears long flowery dresses. She once told a journalist that she could never have a lover who ate meat.

She is in London to promote her band's final album (10,000 Maniacs Unplugged, reviewed opposite); you are therefore expected to talk to Merchant about music and politics and important things. You are certainly not expected to question her about trivial matters like the rumours of her romantic involvement with REM's Michael Stipe.

But Natalie Merchant walks into a Thai restaurant in Soho with short hair, wearing a short skirt. OK, so her shoes are sensible and her skirt is grey, but she is wearing make-up. NATALIE IS WEARING MAKE-UP!! Perhaps I am looking too closely at her pink lipstick, because she quickly points out that she has just been filmed for a television show. "I don't normally look like this," she says, rubbing some blusher off her perfect, heart-shaped face.

You can see why so many college students have fallen in love with Merchant in her 13 years as the thinking boy's American pin-up. She is pretty, with thick black hair, big dark eyes, and pale skin, but she is also sensitive, thoughtful, and rather studious - the sort of person who writes a song called Jezebel after reading Madame Bovary and Anna Karenina.

Merchant is 30 this week, and clearly aware that it is "a rite of passage . . . I'll own my first home; I'll not be a member of the pop band that I've been a member of since I was 17 years old; I've parted company with my manager who I've been with for 10 years - so there's a lot of serious life changes."

She made the decision to leave 10,000 Maniacs two years ago, but told the rest of the band that she would stay with them until she was 30. She says that if pop groups are like marriages, she had been a teenage bride - "Though more than having four husbands, I felt like I had four elder brothers." She didn't like being the only female, especially on long tours. "I was extremely withdrawn." From Irish descent, she was raised a good Catholic girl in Jamestown, a declining steel town in upstate New York. The third of four children, she sang in the local church choir. "The music was really awe-inspiring as a child . . . I loved singing in Latin. And it gave me a sense of history." Catholicism, she says, not only gave her a love of music, but also "an appreciation for concepts like self-sacrifice and giving and humility" - tenets that stayed with her despite five years of nihilistic confusion in early adolescence, when her mother remarried an atheist. (He was, says Merchant, a sculptor and a photographer and a writer, and a nudist Republican.)

Merchant met the rest of 10,000 Maniacs when she was at college in Jamestown. They listened to punk, reggae, folk music, and developed a distinctive musical style: perky, melodious guitar rock, overlaid with Merchant's eloquent lyrics about depression and injustice and other sad things. They signed to Elektra in 1984, releasing four records that gathered good reviews, and a growing audience (Our Time In Eden, which came out last year, has sold 1.5 million copies). The band had something for almost everyone, especially Americans in their twenties: a cute lead singer, nice tunes, social concern. Although Natalie Merchant is undoubtedly serious, she is also rather cheerful. She talks about her pleasure in the new album, her delight in making enough money to buy a house, her enjoyment of her devoted fans. "The one thing that I know about them that is pretty constant is that they are people who I would like to be friends with. They are very thoughtful, very considerate, very gentle, very liberal."

Unfortunately, a few of her fans are not so likeable: the obsessive, scary ones who develop fixations about Natalie. "I've had them on my front porch at 3 o'clock in the morning." Then there are the ones who don't agree with the mixing of politics and music at her concerts. "Once, during the Gulf War, I made a comment about 'smart bombs' - to give a weapon of destruction a name like that was really cynical. And someone in the audience said, 'Just sing your fucking songs - you don't know anything about the war'". Merchant responded by explaining that her sister served in the American airforce, and was, at that moment, in England on 24-hour alert waiting to go to the Gulf. But being a person who believes in the value of constructive debate, "I handed him a microphone and said, "Number one, we don't need to use profanities to express our views here, I think you're a little smarter than that, and let's have a discussion about it . . .". So we had this argument and he said, 'Sing music, that's what I'm here for.'"

Merchant is probably still trying to work out exactly what she is here for. She doesn't like the labels that journalists have attached to her and 10,000 Maniacs in the United States. "We've been called the Fairport Convention of the Nineties, the Fleetwood Mac of the Nineties - that makes no sense to me. I've been the Emily Dickinson of Rock, the Flannery O'Connor of Rock, the Audrey Hepburn of Pop." No one ever writes anything sensible or insightful about her, she says. In fact, she feels like a woman apart. "I find 20th-century media culture to be extremely vapid, and I don't want to attach myself to that." But she's not really sure where her cultural roots lie. "I'm not Italian or Irish . . . I think I have more in common with Seneca Indians than with southern Mediterranean people. I grew up with the scent of the forest in spring, with deer and raccoon . . . It's a really odd thing to grow up with, not knowing who you are, and trying to invent yourself."

She asks me what I think her image in England is. A bit of a hippy chick, I venture cautiously. Interested in ecology, good at writing songs, that sort of thing. And then there's the Michael Stipe question. People are always interested in that. I expect a glacial stare, but she is utterly charming. "Maybe we should just come out and tell the truth about it. I think the reason we don't is that it would just disappoint everyone. We dated on and off for three years - but it was so long ago, it's just ancient history."

Her press officer decides that it is time to finish. Merchant picks up her bag and her coat. "I didn't have a chance to tell you who I am," she says. "You'll have to draw your own conclusions."