James Morrison. Take That. Anything cheesy. Kylie Minogue. Anything you can dance to. Muse. Kasabian. Stereophonics. Anything, really." Katherine Jenkins is reeling off a list of the music she likes best. Any classical? "Oh yeah. I love Placido. Maria Callas. Bryn Terfel. Cecilia Bartoli. Renée Fleming." You can't really blame Jenkins, at 29 years old arguably the most successful classical artist this country has ever seen, for preferring to unwind to a spot of Take That over La Traviata. And who cares if she names fellow superstars over composers when you ask about her classical preferences? Well, lots of people actually. Jenkins's musical credentials – or lack of them – cause near endless hand-wringing in the stuffier enclaves of the classical world.
Every triumph – a record-breaking $10m deal with Warner Music, four million albums sold, consecutive No 1s, a brace of Classical Brits – plays out to a discordant backing track of gripes. Jenkins is, her detractors sniff, an under-trained starlet who has the temerity to sing using a microphone rather than her diaphragm; Classic FM made voluptuous flesh. As The Guardian puts it, writer's quill quivering with indignation, "calling Jenkins's music 'classical' is to test the limits of the Trades Description Act". Her latest venture, ITV's Popstar to Opera Star, in which she mentored faded chart stars as they attempted to sing arias, drew yet more stinging criticism. "It would appear Ms Jenkins has never appeared on the operatic stage", wrote Philip Hensher in this newspaper. "Is it too cruel to wonder whether... she has ever actually seen an opera?"
Jenkins rolls her huge, immaculately inked eyes. "We don't think people really got the idea. We never once said that within six weeks these people are going to be singing at Covent Garden. It was meant to be fun." And the niggling that she's never sung an opera? "I have never said that I'm an opera singer, that's one thing that really grates me." She gives a sigh which she tries, half-heartedly, to turn into a laugh. "I sing opera arias when I do concerts, I put them on my CDs, I trained at the Royal Academy. I've always said that I count myself as a classical cross-over artist. To be a cross-over artist, you have to have the core classical training, which I did for many, many years, but also be interested in the pop side of things. You can fit in somewhere in the middle. I feel I do that really well."
Ever since her debut, singing "Worms", aged four, in her school talent show – "The audience", she recalls, somehow, "erupted into applause" – Jenkins has been an unashamed crowd-pleaser. To say that she does crossover "really well" is an understatement; every aspect of her image hums with all-round appeal. Her journey from church choir to arena has buckets of home-spun charm sprinkled with a touch of stardust. Her ever-growing repertoire ranges from Carmen to "Cwm Rhondda", from Lionel Richie to Andrew Lloyd Webber. Her album-sleeve looks range from barefoot girl-next-door to tabloid-friendly, "diva-statingly sexy", with the result that little girls want to be her, middle-aged women want to mother her and their husbands want to marry her. She's both the official mascot for Welsh rugby and the unofficial Forces' sweetheart.
The only bum note was last year's scandal when she admitted, in an interview with high priest of the celebrity confessional, Piers Morgan, that she had experimented with cocaine. The story seems only to have strengthened her brand, balancing the voice of an angel with something edgier. "I really thought when I did it, 'OK, this could be the end of my career'," she says. "I wasn't surprised by the big reaction to it, but I was surprised that people were so quick and lovely in the way that they supported me. Since then, things have changed – in a good way." The "Sordid Drugs Past!" headlines were a little over the top, after all. "It was written like it was more of an issue than it was – because it was literally just a couple of experimental... it wasn't that big a thing. People see you in long dresses, singing in a certain way and you're put on a pedestal like you have never made a mistake in your life. I did start to find that quite difficult. I'd read articles about myself and they'd say, you know, 'perfect', 'voice of an angel' and I'd think, God I don't think they really understand me."
With that messy business out of the way, the queen of cross-over is free to focus on the next step: world domination, or thereabouts. She has just completed a UK tour, selling out stadiums with a sort of classical Cirque du Soleil show which saw her belting out arias while swinging from a trapeze. This week she released her seventh album, Believe, which includes the title ballad from Love Never Dies. Andrew Lloyd Webber invited her to his house to ask if she'd be interested in recording the song. "I said, 'Well let's just sing it now. Let's get round the piano.' So I sang it to him and he said 'the song's yours'." Would she ever do a West End musical? "I would, but not now. Maybe in years to come. I haven't got the time to be dedicated to something like that."
For now, Jenkins has her sights firmly fixed on America. She is "international priority" at Warner this year which, for her, means being on a plane all the time, and for the company means making Jenkins, at £5.8m for five albums, the most expensive classical signing of all time, work for her money.
"Nobody knows me", she says. "I'm realistic that it's a big undertaking and it might not work." Her team to crack America includes Madonna's publicist, Liz Rosenberg, and David Foster, the platinum-plated producer behind Celine Dion, Michael Bublé and crossover stars Andrea Bocelli and Josh Groban. Jenkins is clearly being lined up as their female equivalent and as such has been touted around various gigs from galas in Vegas to an impromptu, jet-lagged performance of "O Mio Babbino Caro" at Barbra Streisand's birthday party. "All the way through it, I could see Barbra, stroking her dog, Samantha, just watching me".
Believe is her bid to become the global princess of popera – "it's probably the most commercial-sounding album I've ever made" – a smooth line-up of ballads and pop songs (and an inexplicable cover of "No Woman, No Cry") delivered in her rich mezzo-soprano.
It's a businesslike approach and today, Jenkins, in person an appealing, if unreadable mix of sweet and steely, is dressed for business – pristine blonde hair pulled back in a high ponytail, airbrush-perfect make-up and a designery ensemble of towering heels, tight black trousers and power-shouldered jacket. "Although I love fashion, I try and think, 'OK, is this suitable for you and what you're doing right now or are you just trying to follow everyone else?'", she says primly. "I like to try and always be classy. Record companies always try and have their input. Sometimes there's a way of them pushing that skirt a little bit shorter. You know..."
Sing-song voice and doe-eyed smiles aside, Jenkins clearly likes to be in control. "Yep. You have to oversee everything. I don't really want to be the puppet that's told 'wear this' and 'sing that'. That's not me." It's certainly not. Though it drives the groundsmen mad, she always insists on wearing her "Millennium Stadium heels" whenever she's invited to sing the Welsh national anthem from the centre of the hallowed rugby pitch. "I don't own a pair of flat shoes".
She operates a strict regime for her voice – no spicy food ("acid reflux!"), no dairy ("for clarity") and she doesn't drink for a week before she's performing. At this year's Brits, she got all dressed up in McQueen, called into Jay-Z's party for half an hour and went home. "It's a rare thing that I go to parties anymore. If I know I haven't got to sing and it's planned, I can go out and enjoy it properly. But other than that, it's in and out." She practises most days in her music room at home. "And I like to do all my vocalising in the shower in the morning". I have no idea what this means. "You remember to clean your teeth", she says patiently. "I remember to do these things."
She's equally strict when it comes to her private life. She met her boyfriend, Gethin Jones, when the Blue Peter presenter was competing on Strictly Come Dancing and she sang on the show. "We're not together for any publicity reasons!" she says. "Things are going well. We just don't talk about it because you've got to draw a line." It can be quite hard to draw a line when you have paparazzi parked permanently outside your house, though. "I'm not moaning", she says. "It just becomes a bit unfortunate when you have to start thinking, 'do I really want another picture of me without make-up on?'"
There are upsides. This week she has five albums in the classical top 40; her first, Première, hasn't left the charts for nearly six years. Given that her first record deal, aged 22, was for a million pounds, she must be pretty rich by now? "You don't get a million pounds straight off", she points out. She did, though, treat herself to a grand piano when she signed with Warner and her North London home has a whole room set aside for her couture stage dresses. "I'm still pretty reasonable. My mum taught me to be sensible with money."
The green, green grass of home is never far from Jenkins's thoughts. She grew up in Neath, where her mother worked as a radiographer and her father worked in a factory. The whole family sang in the church choir. When she was 11, Jenkins won the Welsh Choirgirl of the Year competition. "Looking back I think, 'how did I not get bullied?' There's nothing that makes you stand out more than singing to your year in assembly on a regular basis." Her parents were encouraging, rather than pushy, driving her around to sing at weddings and with male-voice choirs at the weekends. Did they think she'd be a star? "My Dad did." He never saw it happen, though, dying from lung cancer when she was 15. Jenkins, a straight-A student, went through a brief "stroppy" phase after his death. Her mother wanted her to go to Cambridge but Jenkins, itching to sing, won a place at the Royal Academy when she was 17.
She planned to spend a couple of years after graduating teaching in order to earn enough money to enrol on the opera course. "I was too young. My voice wasn't quite there", she says. "I thought maybe I'd be lucky enough to get into an opera chorus and slowly, slowly work my way up. I didn't think I'd have a career until I was at least 30."
Of course, it didn't quite work out that way. A producer friend of her then boyfriend (Steve Hart of boy-band Worlds Apart) passed her demo onto Universal. Within half an hour of meeting her, they'd signed her for six albums. "I knew people made albums but that's not discussed at a place like the Academy." She'd like to go back there now and teach students about the business.
She's still learning, too. She fits in lessons with her old teacher Beatrice Unsworth whenever she can and (how glamorous!) Placido Domingo has been tutoring her on the side. "It's the best thing ev-er", she whispers. "He's like, 'You should be doing opera! You study with me and we can do this!' If he thinks I can do it..." Her dream role is Carmen. "It's always been something I've wanted to do. I know when I do it, I'll get slated." Carmen at Covent Garden? "Oh gosh, I don't know. I'd love to. We'll see."
'Believe' is out now on Warner Bros Records