Minutes into my meeting with Myleene Klass in her dressing room for BBC1's news magazine programme The One Show, she gives me an exclusive. "It's a girl," says the 29-year-old Hear'Say star and classical pianist turned broadcaster and M&S model, referring to the baby she and fiancé Graham Quinn are expecting in five weeks' time. "We're delighted because we both really wanted a girl, but finding a name is proving tough. Graham thinks I keep coming up with ones that sound like Vegas showgirls or Austro-Hungarian aristocrats, and the names he picks have no vowels, because he's Irish."

She gives an unforced, infectious giggle. I very quickly find that I like glossy, smiley Myleene a lot, for reasons that have nothing to do with her infamous shower scenes in I'm a Celebrity ... last year. The weird thing is that women have come to like Myleene, too.

Partly it's her very public pregnancy. Myleene has done for pregnancy what Kate Moss did for skinniness. The M&S advert featuring her rising from the waves, womanly and five months gone in a white bikini, made swimwear fly off the shelves, and contributed vastly to the high street chain's ongoing financial recovery.

"The great thing was that those who knew I was pregnant thought, well, if she looks all right, I can probably wear it too," says Myleene, "and those who didn't just thought that curves were back." Throughout her pregnancy she has maintained a phenomenal and very high-profile workload, as bubbly co-host with Adrian Chiles of The One Show five nights a week, presenting a pop show on Capital and a classical show on Classic FM every Sunday, and releasing Myleene's Music for Romance, the first of a series of pop-classical CDs as part of a £1 million deal with EMI.

The latter even brought her into conflict on the Today programme with the Evening Standard's music expert Norman Lebrecht, who took a witheringly highbrow line with her, perhaps unaware that he was assailing someone approaching national treasure status. "I love Norman, he's yin to my yang," she says. "I think there are certain parts of the classical world that are laborious and staid and need to jump into the 21st century, whereas Norman's a purist, the kind of person who will keep the viols alive, and the oboes in their uniforms, and will go to the Gramophone Awards, which make me reach for the razor blades. The great thing about Norman is he has passion: he thinks classical music is hitting too much of a common ground, but I think classical music should be for everybody. He disagrees with me, which is fine: I'm sure he shifted a few albums for me, that people bought it just to spite him."

Myleene is already laying plans for further CDs, and a return to work as soon as possible on her other jobs after her baby is born. Indeed, with five weeks to go, she's in no rush to stop working yet. "I'm doing M&S's autumn advert when I'll be eight-and-a-half months pregnant," she adds, "if we can work out a way to get me to Venice. They've made me something to wear that's not a maternity dress, and I think it's great they'll have a heavily pregnant woman who is not a model next to all these supermodels like Twiggy and Erin O'Connor. But it looks like it'd be quickest for me to swim there. It takes four trains otherwise, and Gray has to come too because he'll have to get me back if anything happens."

Although the first three months of pregnancy were "a nightmare, I couldn't get out of bed for love or money", the rest has been "... grand. I haven't even had any unscheduled visits to my doctor. I did ask him if I should worry about working too hard, and he said, the only person who can know is you."

Her pregnancy has also completed the turnaround in the public's perception of Myleene Klass, which has been as remarkable in its way as Marks & Spencer's recovery. When she took part in the reality show Popstars and became part of its manufactured product, Hear'Say, back in 2001, Myleene, with her classical training from the Royal Academy, was cast as the snooty Goody Two-Shoes who was always bossing Kym Marsh and Suzanne Shaw around. When Kym then left, Myleene was blamed, and when the band split after two years it was attributed to her "bitchiness", a suggestion that led her to break down in tears on the Frank Skinner show ("... and then I had to sing I Will Survive").

She was abused, spat at, even happy-slapped in the street by so-called fans. Having gained weight through Hear'Say's diet of takeaways, and been heckled at concerts for being "fat", Myleene dieted down to a size eight and was criticised again for being a bad role model. She was allegedly dropped by Universal after her first solo CD, Moving On. And she finally seemed doomed to tabloid ignominy when it was revealed that Graham, now 34, whom she met when he was Hear'Say's security and touring manager, had been arrested in Ireland aged 17 in possession of £2,000 worth of heroin, and could technically be said to be on the run. It feels wrong to rake all this up again but I ask Myleene if it's true she really was a bitch in the Hear'Say days.

"I definitely needed to lighten up," she replies without hesitation. "I'd been to music college, and worked in orchestras in the West End, where if the curtain goes up at 7pm, they mean 7pm. Suddenly I was in a world where we had a rehearsal booked for 10am, but people wouldn't get up before 11am, then meander in at noon and just mark it through. It drove me mad and I could not understand it."

The rift with Kym Marsh was unfortunate. "In the band, we were absolutely tight, because we were the eldest, and one of the reasons Kym is still working, unlike some of the others, is she's a workhorse. She used to get into work earlier than me, because she had young kids - I understand that now. The stories of rivalry came out after she left, and we got a new member in, and that was really sad, because we had been so close in the band. At the time it was heartbreaking, but looking back I realise it was just like something out of a playground. Now when we meet, I'm a mum-to-be and she's a mummy. I'm also godparent to Suzanne's baby."

When his past connection with a drug gang was unearthed, Graham Quinn was painted as a dodgy type who had leeched onto a popstar, but he sounds, from everything Myleene says, like a rather sober, straight sort. His past was not, as has been reported, a surprise to her. "I knew. I'd like to think I'm not an idiot," she says. "He had to discuss it with all his employers and I was one of them. So he told me about it and I thought, who am I do judge someone on something that happened before I knew them? What I really admired was that he held his hands up to it, and admitted it was his fault, and then later he went back and fixed it." Quinn did, indeed surrender himself to the Irish authorities, and was given a fine, a suspended sentence, and a glowing report from the judge. In addition to running his own security company now, he is patron of the charity Drugsline. "When it comes to this little one growing up, he's going to be wise, not oblivious," Myleene says, tapping her stomach.

When he first signed on with Hear'Say, all three girls fancied Graham a bit, and it was only after a couple of weeks that Kym and Suzanne suggested he'd be ideal for Myleene, who says that a previous infatuation with a Russian classical musician had put her off musical obsessives for life. "What we all liked about Graham was that he wasn't a yes-man, he was this strong, fiery, very grounded Irishman," says Myleene.

Graham was the one who called her "Boney M" when she lost too much weight, and pointed out that her friends no longer felt comfortable hugging her because "I had become really gawky and awkward". There will, she promises, be "no faddy diets, none of that nonsense" when the baby is born. "I'm as prey as anyone to images of super-skinny women, but it's important that women see someone who's normal," she says. "I'm 5ft 5in and I've got boobs and a bum. I'm never going to be tiny-tiny but the best things have happened to me when I've been at my heaviest, including meeting my fella when I was size

16. He pointed out to me last night when he was rolling me into bed - we live by the Thames, so there are a lot of whale jokes in our house - that I was heavier when we met than I have been while I'm pregnant."

She and Graham plan to marry next year, although nothing has been booked. "We've been really lazy and rubbish about it, but I so want to marry him," she says. He wants six children, she'll settle for two. They are currently renting a flat, having sold the two apartments near Tower Bridge that Myleene bought with her Hear'Say swag, and bought a half-completed, five-bedroom house - Graham is overseeing the building work - near her parents in north London.

If there is a second support strut to Myleene's l i f e, a long with Graham, it is her family. Her father, Oscar, was an Austrian navy diver who is now a plumber, her mother Magdalena a Filipina nurse who gave up her job to look after Myleene and her younger siblings, Jessie (now a TV producer) and Dom (an actor and martial artist). Although she was bullied at school in Gorleston, Norfolk, where her ethnic mix "did not compute", she had an idyllic home life and was an unashamed daddy's girl. Oscar raised all his children to be hardworking, and, as Myleene puts it, "in an old-fashioned, navy way, to always be able to buy our own rounds".

He passed on to Myleene a love of engineering as well as music - she considered the former for a degree before plumping for the latter - once let her steer his ship up the Suez Canal, and taught her how to navigate by the stars. For some years now Myleene has been taking an Open University degree in astronomy. She has visited both the Greenwich and Vatican observatories ("I saw the Pope's bathroom!"), and Colin Pillinger, the scientist who launched the Beagle probe, helps her with her homework via email.

I wonder if she sees any split between the highbrow side of her life, the astronomy and the classical music, with the flash-in-the-pan glamour of pop and television and bikinis in the jungle. "There's no pull between the two," she says. "But I believe to make a career today you have to be like water, and find the cracks. Being pliable will get you there in the end."

Where is "there", I ask? Is it being a TV presenter, being famous, being the saviour of M&S? "All I ever wanted to be was a musician," she says. "But everything that has happened since I came out of the jungle has been pretty amazing. It was Graham ' s birthday yesterday. I made him a card and gave him a bag of jelly sweets and a framed photo of one of the scans of the baby. We stayed in and had a curry and a chat, just reviewing things. And I realised I'd be happy to stay like that for ever." She cradles her baby bump again. "I'm pretty content with the way things are right now."