The Sugababes first hit the British Top Ten eight years ago and this autumn, thanks to the soon-to-be-ubiquitous party anthem Here Come The Girls, will be all over it once again. Nothing so strange about that. As we know, the accepted life cycle of a successful pop band is this: an initial run of fame ends in a messy break-up; there are solo ventures that spark briefly, then fizzle; the wilderness years prompt an eventual, sheepish reunion that precipitates (ta-da!) a return to their former glories. We’ve seen it play out many times. Except that this particular act missed the whole mid-section out. Here is the group that defied its own expiry date by never going away.

Keisha Buchanan, now 23, is the sole surviving member of the original line-up (first Siobhan Donaghy and then Mutya Buena left and were replaced, of which more later). Having joined in 1998 aged 13, her only experience of the working world is being in an act shortly to release its sixth studio album and one that has rarely been out of the charts. Subsequent co-optees Heidi Range, 25, and Amelle Berrabah, 24, are a little more experienced in that sense, but, like Buchanan, always dreamed of singing stardom. Each, when I meet them individually, will offer up a variation on, “This is the best job ever.” Legions of envious young girl fans would be sure to agree.

Except that it’s no longer just the pocket money vote that keeps the trio afloat. Through the years, we’ve become used to British girl groups falling short of the standards set by their super-accomplished American counterparts. Even in the case of the Spice Girls, part of the initial charm was that any ordinarily attractive, half-way talented 20-year-old might imagine herself having been invited to join their fledgling line-up. Vocal expertise and a built-to-last, appeals-to-all-ages repertoire were not part of the plan. Yet attitude, tight harmonies and the irresistible force of hits such as Push the Button, Red Dress and Hole in the Head have put the Sugababes in another place entirely.

What they make, at their best, is great pop music, which is why we find ourselves in a converted church in London NW10, celebrating past achievements and what looks like an even brighter future (industry predictions are that Here Come…, which reworks the Ernie K. Doe song heard recently in Boots commercials, will be their biggest single to date). And here they do come, fresh from three hours in hair and make-up (“You don’t get a bouff like this in half an hour,” Range reminds me, stalking on five-inch heels), modern, multi-ethnic young British womanhood personified, albeit given a modishly retro Sixties twist. While the inspiration for today’s shoot is that decade’s filmic kitchen-sink drama, the vibe is infinitely more A Taste of Honey than it is Up the Junction or Poor Cow.

Temporarily, the ’babes are forsaking their own trademark style (part street, part WAG-alicious) in favour of elegant daywear from upscale labels such as Temperley, Versace and Paul Smith. Range is in dressing-up box heaven. Demure in Asprey, she says, “I’m sure me mam hated it, but when I was a little girl back in Liverpool, my sister and I would empty her wardrobes, lay all the clothes on the bed and play shops. I loved putting on her dresses and high heels and today feels a bit like that.” Right down to the wrong-sized shoes, in fact. “Look! They don’t fit at all! I’ve got tissue stuffed in the toes and still there’s still a great big gap at the heel!”

Doing a similarly sterling job of standing upright against considerable odds, bandmate Berrabah recalls the advice she was given by Buchanan and Range (who joined in 2001 aged 18 as replacement for first departee Donaghy) when she herself was invited to join the ranks three years ago following Buena’s decision also to leave in favour of a solo career. Chief among it was to expect not just to be misquoted, but to be the subject of wholly fictitious media stories. And has she been? The reply is a Barbara Windsor-ish (Carry On… era) titter and a vigorous nodding.

“After the premiere of the last James Bond film, I took my mum to the after-party and it was said I was tickling wotsisface’s elbow [Daniel Craig’s] and asking him where he was going on to when his partner turned up, causing me to leave, ‘red-faced with embarrassment’. I never crossed his path! Then I was supposed to have sent a cake to Justin Timberlake’s hotel room… My boyfriend was like, ‘I read a real funny one about you today.’ He knows it’s rubbish. You just have to hope everyone else realises that, too.” All part and parcel of the (best) job (in the world) she reckons, the one she fantasised about when still a kid living above her Moroccan parents’ Aldershot kebab shop.

“I remember my sister calling me down to watch the Spice Girls when they appeared on TV for the first time.” While her own musical tastes aligned her more with the short-lived US R&B act TLC, she loved the Brit girls “from the word go, especially that they all had different personalities and were not so polished. Cheesy, but still there was something there.” So if she had to define herself in similar terms (Baby Babe, Posh Babe, etc), what would she be? “I’m just the nice, bubbly one. I’m truthful and straight. If you’re my friend, you’re my friend for life and I’ll always stand by you.” And people see you as? “Hot, I suppose. Which is completely different to how I view myself.”

The departures of first Donaghy, then Buena, and the subsequent conscription of Range and Berrabah as replacements were made much of in those areas of the media that care about such things (fan websites were awash with rumours of betrayal, bitchery and bullying), all of which would seem to weigh heavily on the young shoulders of the one Sugababe with an unbroken record of service. “Yes, it’s a great achievement to have stayed in the game for so long, but I’ve definitely paid a high price,” says Buchanan, unswayed by exclamations of how amazing she looks in a Ferretti dress. “People will always think it was I who pushed the others out to get my own way.”

Range has already told me she and Keisha asked the newly arrived Berrabah what she thought the two of them might be like to work with: “And she was really honest, saying that after all that had been written she expected us to be horrible and was building herself up ready for that. But we’re not. We don’t fight. We get on. We’re nice people.” Buchanan, distracted because she is getting reports that a childhood friend whom she has helped financially may be shopping a tabloid story against her, appears wearied by that reputation. Not even fabulous clothes can wholly lift her mood. “I worry about stuff,” she says. “I’m a lot more sensitive than people give me credit for.”

All in all, it’s just a bigger, blingier version of the politics of the playground or the office watercooler, and makes the Sugababes seem like any other posse of girls in any other British town. Except that they’re major pop stars with, as Buchanan is at pains to point out, a guiding hand in their destiny (they co-write the hits, choose producers, have responsibility for their own vocal arrangements). “If I’m honest, for every negative there are 100 positives,” she says, rallying. “At the end of the day, this is the best job…” In the world, as we know.

Here Come the Girls is released on October 6. The album Catfights and Spotlights follows on October 20

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