The Sugababes are running late. One is booking a skydive, another has stopped for a bacon sandwich and the third is rowing with her boyfriend.

At least they're not arguing with one another. Pop's most volatile divas are known as much for their bickering and break-ups as for their hits.

When the girls arrive the atmosphere is tangibly different from when I've met them in the past. This must be down to the fact that there's no one left from the original catty line-up.

The new line-up: Amelle Berrabah, Heidi Range and Jade Ewen

So, on the face of it, is one Sugababe interchangeable with another? And is this a band or a brand?

The group was created in 1998, when best friends Keisha Buchanan and Mutya Buena met Siobhan Donaghy and signed their first record deal aged 13.

But amid stories that in-band bitchiness was pushing her over the edge, Siobhan fled in 2001 - never returning from the loo during the middle of an Australian tour.

Ousted: Keisha Buchanan

'Being in the Sugababes made me feel like a zombie. I learnt a lot about how awful people can be,' she claimed, pointing the finger at Keisha.

She was replaced by former Atomic Kitten Heidi Range, 26, who subsequently spent most of her early months in tears.

Mutya walked out in 2005, saying she had always hated her bandmates, to be replaced by Amelle Berrabah, 25. Keisha was then ousted in a dramatic showdown, and replaced with Eurovision Song Contest singer Jade Ewen, 22.

Bitchiness has always been the backdrop to the Sugababes, but it seems that the common denominator for trouble has gone. Heidi and Amelle now say they are happy for the first time.

The last time we met, the girls were in their third line-up and vowed that they'd put their bust-ups to bed.

Keisha apologised for being a jealous bully, insisting they would be grown-ups from then on.

She admitted: 'I was a bitch to Heidi at first because I couldn't get over the fact that we'd worked since we were 12 and this beautiful girl from stage school had it all handed to her on a plate. I made her life hell. That's when I said to myself: This is stupid.'

But in spite of Keisha promising things would change, they didn't, and she herself was forced out.

Heidi says: 'Now we're all on an equal footing. Before that, we never knew from one day to the next what mood or hurtful comments to expect. The last year was unbearable because it was so stressful.'

Finally, Heidi and Amelle snapped. 'Keisha and I had flown out to Los Angeles,' recalls Amelle. 'Heidi and I had agreed that I would have a chat with Keisha, give her one last chance.'

But when Heidi arrived she saw that no progress had been made.

'We realised that nothing was going to change,' she says. 'We told our managers that we couldn't face another day'.

Second line-up: Mutya Bueno, Heidi Range and Keisha Buchanan in 2004

But events took an unexpected turn. 'Our managers told us: "We want you both to stay". The next thing, Keisha was gone, and we've not heard from her since'.

Keisha has since admitted to being a 'hard nut', but has denied that there had ever been any bullying in the Sugababes.

Meanwhile, new member Jade Ewen was on the verge of launching a solo career, when her life turned upside down.

'I woke up to one of the Sugababes' management team shouting through my letterbox.'

'I opened the door and there she was, breathless, saying: "If you would like to be a Sugababe, there's a spare place. If so, you've got to catch the plane to LA now."

'I realised that this was an opportunity I couldn't afford to miss. But I'd blown any chances of a solo career by taking off like that.'

The new trio shot a video and within three days had recorded 12 album tracks. The release of the album, Sweet 7, next month and a series of racy routines have made the new line-up more determined than ever to make an impression.

'We are back with a vengeance, stronger than ever,' insists Amelle.

But an embittered Keisha has claimed that the Sugababes don't technically exist because there are no original members. Mutya says she wants to re-form the original line-up.

So what of the future? 'We'll go on and on,' says Heidi. 'The Sugababes has never been about just one person.'

• The Sugababes' single Wear My Kiss is out now, and their new album, Sweet 7, is out on March 8 on Universal Records.