The three girls on the south London station platform couldn't have been more than 13, and as they waited for the train, they were singing, "My humps, my humps, my lovely lady lumps, check it out!" Though too young to have any lumps to speak of they sang with gusto, until one of them self-consciously giggled, "It's an awful song."
That was last autumn, and the tune was My Humps by the Black Eyed Peas, which reached the UK singles top three. "Awful" was the least of the criticisms it attracted - in America, where it was also a big hit, it was accused of "setting feminism back 40 years". Nine months later, the Peas' frontwoman, Stacy "Fergie" Ferguson, rolls her eyes, fed up with the whole thing. It was "just a song" - a light-relief departure from the California hip-pop band's usual "conscious" attitude. By the standards of her life, the fuss was small beer indeed.
Over here, she's perhaps best-known as the subject of celebrity-magazine "steal her style" features that explain how to achieve her "whadaya looking at?" street chic and peak-fitness muscles. In America, she's been a familiar face since she was nine. That was when, as a third-grader from Hacienda Heights, California, she joined the cast of Kids Incorporated, "a variety show similar to the Mickey Mouse Club. It was a great music and entertainment school for kid actors, but I was embarrassed about it [by the time] I was 14, because it was uncool." Her point is proved by a clip that can be found on the internet - aged about 10 and dressed in disco sequins, she belts out Billy Joel's It's Still Rock'n'Roll to Me with earnestness.
Five years of that was enough to instil a rebellious "fascination" with Los Angeles gang members and guns. "Part of my affinity with urban music comes from being on Kids Incorporated, 'cos we used to sit around [between takes] and listen to Chaka Khan and Prince, and I got influenced by all that. Then gangsta rap got started, and I was infatuated with that - maybe that's why I'm fascinated by guns. Guns are beautiful." Aware of how that sounds, she hastily adds: "But I don't like what they do."
Emerging more or less unscathed from her gang phase, she had a brief relationship with another former child star, Justin Timberlake, and then formed a female R&B trio called Wild Orchid. Their initial success didn't last. When the label refused to release their third album, she went into a depression that led to a dependence on ecstasy and crystal meth. Eventually, weighing six stone and also coping with attention-deficit disorder, she "went crazy". This year she told an American magazine that she'd known it was time to quit drugs when she spent eight hours talking to a hamster. Was that true? A hamster? "It wasn't a hamster," she says, her voice dropping. "It was a hamper."
In American triumph-over-adversity style, there was a happy ending. In 2002, after she'd given up drugs and was working as a backing singer, her friend William Adams invited her to join his middlingly successful all-male rap group. It was a turning point for all - Stacy (as she then was), will.i.am and the Black Eyed Peas. Whisking together social awareness, agile rhyming and real instruments - the same recipe that worked so well for the Fugees - their first album together, Elephunk, sold 7m copies and yielded Where Is the Love?, which became the UK's top-selling single of 2003. The second album, Monkey Business, was also a smash, taking the Peas' worldwide sales to 18m.
And now Stacy is "Fergie" ("I was never Fergie before the group, but I wanted a change, because I was new and improved"), the most recognisable member of one of America's biggest hip-hop outfits. Has success been what she thought it would be? Her wide, feline face crinkles with amusement. "I've learned to suck in my stomach when photographers are around. I used to read gossip magazines all the time, but I stopped when I started being written about in them and read incredible lies about myself."
In its way, all of this has set Fergie up for the solo career she's launching this month with The Dutchess. The deliberately misspelled title refers to sharing a name with the Duchess of York, who has asked her to contribute to an educational charity project. "Sarah Ferguson called me yesterday. I was, like, 'THE Fergie?' She was very complimentary and flattering."
Her American label believes she has the potential to give Gwen Stefani, another female on leave from her male band, a run for her money. Like Stefani's LAMB album, The Dutchess is a first-class example of the modern, no-boundaries sound that throws pop, rap, R&B and old Motown into the pot. It might not register with seekers of hardcore urban thrills - as the UK's Blues & Soul magazine says, "This is pop, people" - but it has the makings of a substantial hit.
The record company has great enough expectations to have sent one of its Los Angeles-based publicists to Europe with her while she promotes the album. Even more unusually, he sits in on interviews. This, he says, is to discourage interviewers from focusing on her former drug problem, although she herself has always been candid about it. Perhaps he's there to prevent questions that elicit answers such as this one, from a recent issue of the American US music magazine Blender, which asked who she would most have wanted to sleep with: "Jim Morrison, because I would probably want to do a lot of drugs and have really trippy drug sex. He seems very creative in bed. I like that."
For her part, Fergie insists she doesn't regret her openness. "Being honest is nice," she declares. "It's important for people to know where I've been so they know where I'm at now. It's cool to express myself, but I've had to learn that doing interviews isn't completely therapy - spilling everything about yourself isn't healthy all the time. But I've been through things that have made me a stronger person, and if I can help some people, I will."
How did the drug problem happen? "It was a gradual thing. I got unhappy [in Wild Orchid]. I'm a creative person, and for a while I did the drugs-and-club scene. I had a 'special relationship' with it," she smiles ironically. "But I've been open about it in the past, and I don't want ... I mean, you can read about it on the internet. Voodoo Doll and Losing Ground deal with that part of my life."
Those album tracks, though, aren't among the four songs that the American label is allowing the European media to hear prior to release. "Yeah, I know you haven't heard them, and that's really annoying," she says, genuinely aggrieved. We have heard the amiably dirty, raucous single London Bridge, though. It's already been No 1 in America, where only Anglophiles would recognise the structure in the accompanying video as Tower Bridge. "I knew that," she insists. "I'm not saying it's about the London Bridge, it's just a London bridge."
London or Tower, the song is pretty unambiguous. It's hard to hear the chorus - "How come every time you come around, I go down like London, London, London Bridge?" - as anything but sexual. But, despite having co-written the song, Fergie seems ambivalent about being perceived as sexy. US magazine People declared her one of the "50 most beautiful people in the world" in 2004, and she habitually wears tops that reveal incredibly taut limbs and stomach. But she seems preoccupied by the fear that people will get the wrong idea about her. She wants it known, for instance, that the Jim Morrison comment was facetious: "I'm not promiscuous, and I don't sleep around."
She raises the subject again later, saying she'd like to be "a role model" for girls who might be coerced into having sex too early. "I don't sleep around, and I want to show girls that you don't have to give it away - it should be a precious gift." Fair enough. But how about if she were equally proud of the qualities that make her interesting - her honesty, and refusal to be as prissy and evasive as most American pop singers in her league? And for sticking up for My Humps in the face of criticism, because she liked it? Her publicist could have saved himself the trouble of coming to London. Fergie can look after herself.
· The Dutchess is out on September 18
