Time has been kind to Joan Baez. Over peppermint tea in the restaurant of a South London hotel, the queen of America's folk scene in the Sixties appears extremely youthful for someone in the fifth decade of her career. "We'll sit here until we get thrown out," she says, firmly but quietly, after the manager protests at our not wanting dinner. She appears the model of calm, unwavering serenity, but something about her unblinking stare - and her swift dismissal of a fussy maitre d' - suggests that you wouldn't want to get on the wrong side of her.
Perhaps the company she keeps has maintained her youth. Day After Tomorrow, her new album, is produced by the much younger country singer Steve Earle and it features songs by her favourite songwriters, including the British singer Thea Gilmore, who is half her age.
"Steve's so like me in a lot of ways," says Baez, who holds herself in a poised way that has a tinge of therapy about it (she underwent a lot of it in the Eighties) and reveals an awareness of her status as a diva, albeit one that would rather see the poor clothed and fed than swathe herself in diamonds. "We share the same beliefs, although he's so left of me that I call him Mr Pinko, and there's something about his gruffness and my voice that gels."
Baez is a good advertisement for not getting caught up in stardom. Born to a liberal Quaker family in 1941, she'd already lived in France, Italy and Iraq by the time her Mexican father, a physicist who worked for Unesco, and Scottish mother settled down in Boston when she was 17. It was only a year later that she was thrust into fame after a triumphant appearance at the 1959 Newport Folk Festival. Her first album was already out by the time a young, hungry and extremely ambitious Bob Dylan hit Greenwich Village in 1961.
For a brief moment in the early Sixties Dylan and Baez were the king and queen of the folk movement, the perfect couple to lead the young of America towards a new consciousness. But while Baez stuck to cover versions and causes, Dylan took off on a poetic journey all his own, hitching on the coat-tails of Baez's fame and then leaving her behind to become the foremost songwriter of the 20th century.
"I've never really been a songwriter," Baez says of the path she's taken. "Steve Earle wrote a song for me called I Am a Wanderer that expresses a sentiment I relate to far better than anything I could write."
These days, the warbling falsetto that Baez brought to We Shall Overcome and Babe I'm Gonna Leave You in the Sixties has been deepened by age, but she's still using the songs to get across her core messages of pacifism, social responsibility and, for the first time, party allegiance, saying of her endorsement of Barack Obama: "For years I chose not to engage in party politics. At this time, however, changing that posture feels like the responsible thing to do."
Her strident sincerity is something that doesn't always sit well with audiences as radical politics fall in and out of fashion. "After 9/11 nobody wanted to hear anything bad about America," says Baez, growing animated as she enters into political territory. "Nobody loves a war better than the President, and a few years ago it got to the point where if I said anything I truly believed about the Iraq war or global warming during a concert, people would get up and leave. That's fine with me. Actually, it's a badge of honour."
Baez is used to hostility. One senses that she thrives on it. At school in California she upset teachers by refusing to leave class during a bomb drill, reasoning that if the school was to be nuked, running outside would hardly do anyone much good. Later, as a teenage folk singer she would stop singing and glower at anyone who dared to talk during one of her performances. She and her first husband, David Harris, served jail sentences for their resistance to the Vietnam War (he refused the draft; she refused to pay a portion of her taxes to the war effort). It's no surprise that the rebirth of her career coincided with an increasing dissatisfaction with the Bush presidency and its foreign policy.
"Little by little it became clear that Bush was bizarre - and dangerous," she says. "I would do concerts where I would see people in the audience sitting with their arms crossed, looking angry as I said: ‘I was right 40 years ago and I am right now!' and throw my fist in the air. Now they're listening. Bush's great trick is to suggest that to go against him is to be unpatriotic. Slowly people realised that."
Baez acknowledges that, to her generation at least, she eternally represents the Sixties protest movement. "I'm a part of history," she says with calm resignation. "I represent so much before I've even opened my mouth. But I was more active when I was young, and it's only now that I'm spending time with my family."
Like so many of her contemporaries, Baez put bringing her message of peace to the world before raising kids. When she was divorced from Harris in 1972 their son Gabe went to live with his father, and it's only recently that she has become close to him. "I live with my mother, who is 95, I have a four-year-old grandchild, and it's a turning for me. It's confusing, too - am I really allowed to hang around the home and look after my mom?
"I don't regret what I did in the Sixties, but you can't stay on the biting edge of radicalism all your life. My core beliefs of non-violence haven't changed, but my lifestyle has."
Baez accepts that the Vietnam War and the civil rights movement gave her a purpose, and that when they came to an end she was left floundering. "It's natural," she says with a shrug. "The Vietnamese developed all sorts of neuroses and phobias after the war ended because they were no longer spending every day in the heightened state that comes with not knowing if you're going to be killed or not. When the war ended a lot of us lost direction. I certainly did."
It's also taken Baez a long time to relax and actually enjoy herself. She was, by her own admission, "far too neurotic" to appreciate early fame, and her image as an overly earnest Virgin Mary figure worked against her as the concerned citizenship of the counterculture gave way to hippy experimentation in the late Sixties. "I had this great fear of going commercial. As a result of becoming well-known at such a young age I was afraid of the wider world. But I did also have deeply held beliefs that I clung on to tenaciously. The big event was meeting Martin Luther King in 1956 at a Quaker seminar. That pretty much shaped the direction my life took."
In 1963 Baez was given the job of driving King and Jesse Jackson from an airport to a march. "They laughed all the time and told racist jokes about themselves, and I realised that nobody could see that side of them. They had to be seen as serious, and I related to that. We got to a restaurant and I asked them: ‘Don't you have a big march to organise?' They said: ‘We just have.' You get a public image that you have to live up to but your private reality is often very different."
After years of being written off as an unsmiling anachronism, Joan Baez is relevant once more. She thrives on political and economic tension - such as now. "At times of great uncertainty music and politics are fused," she says. "I would never have sung We Shall Overcome to an American audience during the Eighties because it would have been a nostalgia trip. Now it's appropriate again because it's relevant. I'm happiest when that happens."