Christina Aguilera’s latest album, time-travelling back to Prohibition speakeasies, has gone straight to No.1. Is there nothing the former Mouseketeer can’t do, wonders Dan Cairns.

THE room goes silent. Two dozen record company honchos freeze as the disc containing new tracks by their biggest artist jams in the drive. Is the singer who recorded those songs about to throw one of the wobblies to which she is rumoured to be prone? And who’d be the poor tape operator in these circumstances? Not surprisingly, the young fellow struggling to fix the problem looks mortified. But, turning to him, Christina Aguilera positively purrs: "Take it out real quick," she suggests, "and wipe it off."

If Aguilera had made a remark as innuendo-rich as that back in 2002, how we’d all have sniggered. That was the year when, casting off her teen-pop image, she scandalised polite society with the video for her single Dirrty. With her 157cm frame clad in bottomless leather riding chaps, the singer, rechristened Xtina, preened and pranced her way through a song that invited her intended to "Give all you got/Just hit the spot". On American sketch comedy show Saturday Night Live, actor Sarah Michelle Gellar mimicked Aguilera, saying: "Once people see this video, they’ll stop seeing me as this bubble-gum ho and start seeing me as an actual ho." Speaking about the video now, Aguilera says: "I’ll always back it up, even when I’m 50 years old. Hopefully, I’ll still fit into those chaps."

The songs those label bosses have gathered to hear are taken from Aguilera’s new album, Back to Basics. It’s a mark of her success - more than 20 million copies of her self-titled 1999 debut and its follow-up, Stripped, have been sold - and the clout it has given her that the 25-year-old can get away with releasing a double album.

While disc one (chiefly produced by one of the titans of 1990s US east coast hip-hop, DJ Premier) echoes and thrums with the hooks, beats, power ballads and emotive vocal runs that are her trademark, disc two, produced by uber-hitmaker and long-time Aguilera collaborator Linda Perry, is determinedly retro, going right back to the speakeasies of the 1920s through to the 1940s. It’s far from standard pop fare and, at 80 minutes and 22 tracks, Back to Basics arguably should have been a tough sell.

Standing in front of the mixing desk, Aguilera is doing her best to confirm a reputation for minimal eye contact. She gulps for air; her words fall over themselves. At first her unease seems endearing. Then you catch yourself thinking: maybe those nerves are down not to humility but to the strangeness, the novelty, even, of the situation she finds herself in. Maybe she simply no longer spends time in such untested, questioning company.

Later, in a crepuscular corner of her favoured Beverly Hills hotel, Aguilera says: "There aren’t many opportunities I get, honestly, to mingle with new people because of the trust issues. You never quite get a read on who’s being fake and who’s being real. It’s hard for me to make new friends. You have to understand how many insincere people come up to you when you’re in the limelight."

Her as-yet gentle giant of a bodyguard sits nearby. Eye contact is now full-on. She’s keen to stress that she isn’t complaining - "I can’t sit and feel sorry for myself" - but, although that mingle may not be quite on a par with Liz Hurley’s alleged description of non-celebrities as civilians, it’s revealing nonetheless. She is different from the rest of us. How could she not be?

This is an important moment for Aguilera. However much the label people applaud during the playback, however much she talks about the power her success bestows on her, the singer knows she’s testing new waters with her third album. When I ask her if she considered really pushing the envelope and hang the consequences, the tone of her rhetorical answer is incredulous: "And not worry about having a hit record?"

It’s important in another respect, too. Her career trajectory - a local celebrity in her Pittsburgh neighbourhood; adolescent star, alongside Britney Spears and Justin Timberlake, on Disney’s The New Mickey Mouse Club television show; Grammy-winning breakthrough artist with the smash-hit single Genie in a Bottle; vamp on Dirrty; and emoting balladeer on its follow-up, Beautiful - may have installed her in the most exclusive celebrity firmament. But it has also led many to ask: what’s she all about, where is she coming from and where is she going? So will Back to Basics clear this fog or thicken it?

In the sense that the record covers enough familiar bases for her to get away with the new ones she touches on, the answer would seem to be: a bit of both. But what blasts most loudly and clearly from the album is that extraordinary voice, an instrument about which her idol and friend Etta James has commented: "She’s like somebody that was born at another time, an old soul."

When she started releasing records, Aguilera was ridiculed for her crazed bouts of coloratura. Back then, it seemed as if she had studied Mariah Carey and, on an anything-you-can-do basis, resolved to squeal, ululate and warble her way to the top of the charts. "On my first album," she says, laughing, "Ron Fair (her musical adviser) used to take me on one side and say, ’You know, you don’t have to give it all you’ve got. Hold back a little.’ But it was like being let out of a cage."

Last laughs are Aguilera’s specialty. Having fired her original management team after her debut album and thrown away the pop-candy rulebook they’d written for her, she’s not averse, even now, to settling old scores. Reflecting recently on the labels that turned her down when she first went shopping for a deal, she sniped: "People definitely lost their jobs over that, I later heard." And the new song F.U.S.S., apparently aimed at her former songwriting partner Scott Storch, is unambiguous: "Looks like I didn’t need you," she sings. "Still got the album out."

Add to that a veritable logjam of rumoured feuds with rival singers - including Spears, Pink, Kelly Osbourne and Carey - and her reported insistence on items such as mineral water at a precise temperature, and the D-word looms large.

Ask her now about, say, Spears, and she looks suddenly as if she’s jammed her teeth on a huge speech-stopping toffee. So I switch to the diva question. She started singing in public aged seven, I say. She should be a complete nutcase. Is she? ’No, no, no," she cackles. "I’m pretty down to earth. You could ask my husband. I have some weird insecurities that I’m probably not going to get into; in fact, I’m definitely not going to get into."

Aguilera married Jordan Bratman, a former A&R music executive, last November. You can see his round, bestubbled features in the background of many pap shots as his famously night-owl wife emerges in the small hours from a club. Her horrid grounding in men through her violent father - whom her mother fled, two daughters in tow, when Aguilera was six - caused her no end of problems (the haunting Oh Mother, on the new album, addresses those experiences unflinchingly) and made her, by her own admission, a bad picker.

Her father (from whom she remains estranged) and those wrong romantic choices explain, she admits, the guards she erected around herself and her notorious need for control. Another factor was the bullying she endured from classmates envious of her early success, which included her mother’s car tyres being slashed and the dance floor at her college prom night emptying when her first single came through the PA.

"When you have a difficult childhood," she says, "you never want to feel helpless in a situation ever again. But I’m thankful for the fact that I grew up in a chaotic childhood because it really drives me."

Bratman is relaxed, she insists, about her more risque incarnations. On the new album, they include wonderfully dirty tracks such as the latest single, Ain’t No Other Man and Nasty Naughty Boy; and, on another song, the lyrics "I want to give you a little taste of the sugar below my waist".

When I remark on the last song, Aguilera lets out one of the dirtiest laughs since Carry On actor Barbara Windsor’s heyday. And it returns, gale force, when she discusses her recent purchase of works by British grafitti artist Banksy, one of which features Queen Victoria in a compromising position with another woman.

The woman who once admitted to smashing plates as a form of primal therapy, and who used to run upstairs as a girl and sing along to The Sound of Music to drown out the rows, is now, she says, "in the happiest place in my life". For all the cosmetic costuming provided by her present image of Jean Harlow peroxide and scarlet lips, she looks, finally, as pretty as one had always suspected she was.

People are questioning the authenticity of her shot at what she calls the fun music of her youth, the records her grandmother played by singers such as Billie Holiday, Ella Fitzgerald and Nina Simone.

But what does authentic mean? An original recording presumably fits the bill. Is a new one steeped in that original’s ethos and spirit disqualified? That seems nonsensical.

All I know, all Aguilera clearly believes for certain, all those nervous label bosses are desperate to convince themselves of, is that Back to Basics is an extraordinary album for one of the world’s biggest stars to make. Instead of a cynical, joyless sequence of autopiloted rhythm and blues, the record is a thrilling testament to the power the singer wields, the ambition and talent she has, and the larynx she wraps round the package. Surely this is what we want from a star: a vast-lunged, occasionally stroppy diva with issues; a mass of contradictions with a core of calm certainty; a bod to kill for; a voice to die for; possibly impossible; completely unstoppable.

"It’s my passion, my love," she says. She’s talking about her career.