Do it like Jessie J

So who the hell is Jessie J, anyway? Coming from nowhere, so far this year she has picked up a Brit Award and kept Lady Gaga off the British No 1 spot.

As she sits there, fiddling with the bulletproof fringe you just know is going to be the breakout haircut of 2011, it's clear that Jessie, along with the 16 million people who have watched the YouTube video for her stand-out track, Do It Like A Dude, believes her own hype.

She tells me right away that her motto is "never cater for the handful, cater for the masses".

"I've always dreamt big and that's why I'll say I want to be a UK pop icon," she goes on, popping jellybeans into her vermilion, Chinese-dragon mouth. "I'm going to be in America next year. But I wanted to release here first because this is where I'm from and I feel like I owe it to my people."

Justin Timberlake says she's "the best singer in the world right now", but she can also write a tune, having already penned tracks for Alicia Keys, Britney Spears and Miley Cyrus. In fact, so big has the hype been around Jessie J the solo artist (real name, Jessica Cornish), it's hard to believe she has been on the scene only three months. "But I feel like just this year has been 10 years of my career: the amount I've won, the opportunities that have opened up to me, the people who want to work with me. I'm just, like, ‘Wow!'"

Glee kid

Cornish, now 22, is the first to admit that she's "living the dream". Which means all of the above, plus "finally earning some money and being able to buy myself a nice handbag". She is a Brit School graduate (Adele was in her class) and began her life as a performer on the West End stage, aged 11. She has done "loads" of musicals over the years, and there is definitely something of the Glee kid about her — take away the hip-hop hipster clothes, the Essex twang and the tattoos (featuring lyrics from her songs) and you can just picture her warbling along with Mr Shue and gang. Obsessed with show tunes as a teenager, she says that her musical influences range from Whitney, Mariah and TLC to the stuff her parents were into. "I'm a fan of the best of everything. I'm a huge music lover."

Perhaps it's the confidence she wears like a suit of armour, but Cornish seems way older than her 22 years. She's full of self-help maxims — "I've always said, if I don't believe in me, nobody's going to believe in me" — but constantly reminds me: "I've been doing this for a long, long time.

"I've been a hair model for four years, worked in Hamley's, worked on a market stall. I was in a girl band for two years , been signed twice, got a publishing deal. I've been to Japan, toured the world with Cindi Lauper, Macy Gray, Girls Aloud and the Sugababes."

And she's proud of the graft. Having come of age as an artist while television talent shows played in the background, she says she "recently told Simon Cowell that the reason I never did it is that I wanted to take the hard route. I always felt like The X Factor was skipping the queue."

Plus, she wouldn't have been able to sing her own songs. Having written more than 600 tracks to date, she narrowed it down to 13 for the album, which she says is "the story of me going from a young girl to a woman".

‘Alien'

She constantly quotes from her songs — Nobody's Perfect: "I nearly left the real me on the shelf" — to describe her life, which has been far from one long balloon ride. Cornish was diagnosed with an irregular heartbeat as a child. The beta-blockers she had to take gave her skin a greenish tinge, earning her the nickname "Alien" at school — "Kinda funny now, but horrific at the time." It meant she never smoked, drank or took drugs, apart from when she "accidentally" ate a whole hash cake in Amsterdam while she was there on tour with Chris Brown. "I had to call an ambulance cos I started convulsing. I called my mum and she was, like, ‘I'm glad you did it, because you'll never do it again.'"

Then, at 18, she suffered a minor stroke, at the same time that her initial record deal fell through. "It was like my life was over, but my mum told me, ‘When one door slams in your face, it means there's another one around the corner, waiting to be opened.' And in the end, it was a golden ticket in disguise."

If she already looks and acts like a star (the photographer swoons over her "Versace mermaid" poses on our shoot), she is still adjusting to life in the limelight. Luckily, "there are about five people in my life who I can call any time. Somebody said to me, ‘The brighter your star, the smaller your world.' And that is very true. When you live this life, you need a small group of people you can trust, so you know you can vent and it won't go any further."

And what about a special someone to trust? Telling me not to "put a label" on her sexuality, she adds: "...I've only been in love once and it's the most amazing feeling." There's a long pause when I ask if she's with that person now. "I'm going to ignore that question," she says, but we'll know when she's in love again, "because I'll write a song about it."

Fiddling with her fringe, aligning it just above her flashing eyes, she pops another jellybean into her mouth and deftly changes the subject. "You know, people keep asking me, ‘How does it feel to be on this amazing roller coaster ride?' And I'm, like, ‘I'm still queuing up. I haven't even got on the roller coaster yet. I haven't even started.'"