She's 27. She sold over two million records in three years, making her the fastest-selling opera star since Maria Callas. She's got a £1-million record deal, the biggest in the history of UK classical recording. She's the first person to take up the top four spots on the British classical music charts. She's 83rd on the 2007 Sunday Times Rich List for young people, with a £6-million fortune. She's the only woman to make 'I Will Always Love You' bearable.

But there's a lot more to Katherine Jenkins than figures. Watch her perform live and apart from that voice (which shattered a chandelier when she was 17) you’re struck by just how charming and bubbly she is. Where most musicians limit their between-song banter to niceties and insincerities, the former singing teacher engages in actual conversations with her audience, giggling, joking and clearly having a ball — the complete opposite of the formal classical singer you'd expect.

Jenkins is exactly the same when I ask her about this.

"I love performing live," she says in her distinct Welsh lilt. "I think it's very important when it comes to a concert that the audience feel relaxed and I really enjoy that kind of connection with the audience where you can talk between songs, have a laugh," she adds.

The mezzo-soprano wasn’t always so relaxed — she was "very, very nervous" until her first major show in 2003, a little performance in front of 70 000 rugby fans at Cardiff's Millennium Stadium.

"I was so frightened the week before and I kept having nightmares about the 73 000 people who were going to be there, all the millions at home. I was so nervous.

"But then when I walked down the tunnel onto the pitch all the crowd were singing 'Delilah' by Tom Jones. And it just made me feel at home," she smiles at the memory.

"It's kind of cured me because I don’t think anything's ever going to be as bad as the first time you have to go out in front of so many people."

It also helps having Kylie Minogue on your side — and a little bit of superstition.

"I've gotten into a routine before shows where, believe it or not, I've got to listen to Kylie Minogue," she giggles conspiratorially. "So I've got her greatest hits album and when I'm in hair and make-up I always listen to her.

"And then if there's a choice of bathrooms, I'll just make sure I have to use the same one every time," she laughs, "so you do find the more you do as a performer you get into these little things which in your head make you ready to go out and do a good show."

Those shows keep growing as Jenkins' audience does — thanks partly to her approach of mixing classical music with pop.

"I think people are wrong when they think [classical music is] only for an elite group and it's only for very rich people, very posh people," she reasons.

"They expect opera singers to be really overweight and wear those horns and all that. But that's all so wrong."

No stuffy traditions here.

"I just thought if I could introduce people to it in the right way — if people could identify with the artist and see they were accessible and not feel like there was a barrier up — people would fall in love with it the same way I did," she suggests.

"Part of wanting to encourage more young people to buy classical records, is sometimes taking songs that they already know and giving them a change of treatment like I did with 'I Will Always Love You' — big lush orchestral arrangements, translating it into Italian.

But the approach doesn’t always work — 'Yellow Submarine' wouldn’t really make it as an aria — so Jenkins has to make her repertoire choices carefully.

"There are only a few songs that really lend themselves to that sort of treatment, but I always choose songs that strike me on an emotional level because I have to keep singing these songs again and again.

"I'm a very emotional person, so it has to be something that gets to my heart. Also I look for songs where the words are really inspirational. I think music's a very powerful thing and I get letters from people saying 'It helped me get through losing my husband', or whatever they're going through at that moment.

"So I've always looked for songs with words that would help people, because I've found music to be very helpful to me," she says, absolutely sincerely.

Of course there's been the inevitable backlash from purists fond of pointing out that Jenkins has never actually appeared in an opera.

She's not too fussed: "You can't please all of the people all of the time. I think if you tried doing that it's never going to happen. As long as my fans are enjoying the albums that I make and enjoying coming to see me in concert, that’s all that really matters. I'm not really that bothered what critics think."

Again it's about connecting with real people — much like her involvement with the British Forces Foundation which has seen her perform for British troops in Iraq (twice) and Afghanistan.

"I was doing a lot of concerts to the military in the UK and the press here started to label me the new forces sweetheart which I thought was a lovely thing but I wanted to earn the title, rather than just be given it."

When she went to Iraq for the first time at the end of 2005, the welcome was less than friendly: "We got fired at by a ground to air missile while we were in a helicopter. I honestly thought there and then I was going to die in Iraq because the helicopter just fell out of the sky and we heard all these warnings going 'missile alert: rear'.

"It was horrible."

Seeing the soldiers was the complete opposite.

"It turned out to be one of the best days of my life. I felt so honoured and privileged to be welcomed into the family of the military for that time and to see what an amazing job they do out there."

Her involvement with the troops is but one of her activities outside singing — Jenkins has always had a lot on her plate ("I was such a busy child, after school I'd go off to dancing lessons, singing lessons, choir practice, piano lessons…") so when it came to writing her autobiography 'Time To Say Hello', she had plenty to say.

"It's in some ways funny to me to write an autobiography at 27 and I do think that to some people that might be strange, but I wouldn’t have written it if I didn’t think I had a story to tell," she offers, not unreasonably.

"I wanted to write about how this all happened to me because I get lots of letters from people asking 'How did you get into the music business?', 'How did you get your record contract?' and I want to tell the story now, not in 50 years time. I want to tell people so that my advice might be of help to young people today."

But she also had a more personal story to tell ("It was a great thing, almost like therapy") — like dealing with the death of her father, a factory distribution manager when she was 15.

"I wanted to write about losing my father," Jenkins states plainly, "and what happened to my family relationship. We were all going through different things at different ages, and how we got through that — and I hope that might be of help to some people."

So who does the 27-year-old turn to when she needs help — or just a dose of reality?

"My family are so important to me. They're very much your traditional Welsh family — they will keep my feet on the ground and if I ever think I'm getting carried away and taking [my success] for granted, they will tell me," she giggles again.

But, through the laughter, it's clear she misses her father.

"Because he was sort of the house husband and he spent more time with us while my mum was at work, my dad always made me believe, he had no doubt in his mind that I could get there if I put the hard work in," she recalls.

"And so I think it's a real shame — I think that's my biggest regret that he's not here to see [my success]," she adds, wistfully.

"But I believe that he is as well, because I feel that he's with me in spirit, and somebody's guiding me along this path, so… I definitely feel like he's here with me…"