The artist formerly known as Ginger

It's a fairly safe bet that come 9pm Wednesday evening, there's more chance you'll find Geri singing with the All Saints than curling up for a night in front of the box. Because if she did that there'd be the very real danger of having to endure another viewing of Geri, the one- hour fly-on-the wall documentary by award-winning director Molly Dineen. Dineen says of her complex subject, "She looks at it now and thinks she was barking. She is much calmer now. She doesn't speak 95 to the minute. She has changed since the film was made." Which might be why Geri is, according to Dineen, "gutted" by some of the scenes. But to her credit, she didn't put pressure on Dineen to change any of them.

When Geri left the Spice Girls last May, she decided to ditch the brash ginger streaks for subtler blonde tresses, the spangly stage costumes for Prada black and the good-time-girl persona for something more sophisticated, more discreet.

How else should a girl who craves fame so badly deal with a quiet period of privacy and self-reinvention, away from the media heat? Invite one of the country's leading documentary- makers to record the experience, obviously. Invisibility and introspection filmed for national television really isn't a paradox when you're Geri Haliwell.

And so she invited Molly Dineen to observe her state of limbo; those five months last summer when she was poised somewhere between Ginger Spice and the next reincarnation. "Hopefully people will see what I'm really like; that I am a nice person," says Geri, in the first five minutes of the film and on her way to George Michael's hideaway in the South of France. Suddenly Geri is completely alone; she has to fix her own make-up, make her own decisions about the media, her image and the next stages of her career. Certainly, her autonomy is impressive. "It was so surreal," recalls Dineen. "There was no control at that point, no responsibility, only the grown-up trappings of real money." She was, as Dineen says admiringly, "a real ballsy chick."

In the first few minutes of Dineen's film, Geri stretches her small form over the grey-slate roof tiles of her opulent Paris hotel. She is on the top-floor terrace, staring at the paparazzi below. Geri is keen to peek at the photographers she has supposedly come here to avoid. "Imagine if they got a shot of me," she giggles at the camera. "They'd think I was committing suicide, that'd sell a few papers wouldn't it?"

It is one of the more telling moments in Molly Dineen's compelling documentary. We know, as if we really needed further evidence, that Geri never likes to flee fame's prying gaze for too long. She will, of course, scale ever dizzier heights to guarantee a foothold in the limelight. Others may anticipate her fall but she knows better than to let that happen.

It's hard to know, though, if we're ever viewing the "real" Geri. And it's quite clear Geri's not sure herself. Generally we see Geri veering between manic hyperactivity and little-girl-lost. There she is jumping up and down jubilantly when Sotheby's auctions her Ginger Spice wardrobe for pounds 36,000. Then, minutes later, she's little-girl-lost deflated by her own fame. "I do lead a lonely life. I find it hard to keep up with my friends," she says. "Even my accountant is a good mate. That's why I wanted you to film me, Molly," she laughs into the camera. "I wanted you as a mate."

Which Dineen and Geri did become. "I was the maintenance-husband side of her life. She would lean on me but then I could lean on her. At some points when I was away filming I missed my two-year-old daughter so much and Geri was so supportive."

Dineen was, however, somewhat perplexed by the brand of fame Geri epitomises. She says, "I didn't understand what she's about. I'm from another generation. My idols generally wore very tight trousers and took lots of drugs. This lot are so clear-skinned, so healthy, like machines almost."

After five months of filming, though, their relationship grew less rosy. It seems Geri wasn't so keen to have Dineen around and the novelty of warts-and-all wore a little thin. Skinny and much prettier than her photographs suggest, Dineen, you feel, would be no pushover for the

Spice Girl who was always used to getting her own way. "I wanted to be there when she was feeling insecure and she began to get irritated by it. Our relationship changed - the filming was too much for her." And some aspects of the "ballsy" persona grated. "I was irritated by the hypocrisy and confusion. At times she wanted me to feel sorry for her yet she was constantly pushing [for publicity]. Pushing, pushing. She knows perfectly well what fame is yet she doesn't want to give it up."

Part of the ambivalence may stem from the fact Dineen isn't used to filming young female pop stars. She is, by her own admission, much happier getting under the skin of male institutions. "Filming a single chick was weird. I didn't choose her. I was smuggled with my handi-cam into her bubble," she laughs. "I'm used to filming anonymous people who think they're shit and she was the opposite. The idea of saying 'look-at-me' was anathema to me."

Usually, Dineen sticks to more innocuous subjects, such as London's Angel Tube station and her Bafta-winning documentary about London Zoo, The Ark. Dineen filmed Tony Blair for a party political broadcast, too. She specialises in allowing the viewer to sympathise with characters who can be hard to warm to.

Which may be one reason why Geri chose her. She bent over backwards to be sympathetic. Dineen recalls, "There was one point when she was talking about how she developed from wearing platform boots to lower-heeled shoes. I couldn't put it in. It could have made her look moronic. It's unfair to put some things in - she is so many different things."

You can't help feeling Dineen over-compensates on film for the less generous thoughts she had in private. She seems visibly worried that Geri may not come across as likeable. I mention one moment where she fluffs her lines just before her UN press conference. "There are so many terms," she panics. "Pro-abortion, pro-life. Now pro-life - apparently that means you're anti- abortion. I didn't know that," she says wide-eyed. Molly still has mixed feelings about that scene. "You don't think that's too mean do you?"

They're still in touch, though. Geri recently bought Dineen's daughter a pair of high-heeled slingbacks and a pink fairy outfit. "Every time I see her staggering across the kitchen in all of that I think of Geri." The film is peppered with Dineen's off-camera encouraging comments and at some points you wish she'd prod her subject for more of a reaction. Perhaps she doesn't need to. What comes across - and maybe this is what "gutted" her subject so - is that the main person in Geri's life is Geri. You see that her raison d'etre is publicity; she defines herself in the eyes of others, mainly strangers. At one point, she hangs out of a loo window of a theatre. "Hope you don't get too cold down there," she shouts to adoring weepy fans. Dineen asks her what she makes of the girls crying over a stranger they feel they know. "Perhaps they like me for myself," says Geri sweetly - with total self-belief.

'Geri' is on Wednesday 5 May, 9pm, on Channel 4.