Impossible to pin down in a world of female pop homogeneity, at 22 years of age, Jessie J carries herself with the confidence of one twice her years. She has achieved everything herself, and on her own terms. Singer, songwriter and show-pony, she has the enviable ability to excel at it all.

She’s had to. ‘Look,’ she says, straight off the bat, ‘I had a minor stroke three years ago. I’ve got heart problems. I’ve looked at the big stuff straight in the eye, had people sitting on the end of a hospital bed wondering what’s going to happen next and genuinely not knowing. I don’t drink. I don’t smoke. I can’t touch drugs. I can’t even have caffeine. I have to be confident. Because I can’t intoxicate myself with those props ordinary young people have to give them confidence.’ Amidst problems most teenagers haven’t yet to even consider, music was Jessie’s saviour. ‘When I’m in the studio sometimes, I think no, I don’t need a therapist. I just need to write a great song.’ That’s when she does it.

Jessie J is simply not built as other pop-stars. Quite literally, she stands head and shoulders above her peers. When you hear an echo of Lily Allen’s street slang in her lyrics, you remember this one’s the real-deal, brought up in the inglorious backwaters of Essex and learning her street-smarts on the hop. When you hear a chorus as pop-it-like-it’s-hot addictive as one of Beyonce’s you recall the fact she can’t rely on a hard-fought party-girl lifestyle to support the myth-making. When you hear the pure, flame-grilled sass of her attitude grooving through every beat of her debut album, Who You Are, you might think of Pink for a second; then check the record sleeve and remind yourself this one is cool, too.

This, ladies and gentlemen, is Jessie J. She is her own special creation.

This girl isn’t afraid of pulling herself up by her boot straps and starting all over. ‘I like the hustle. I like the grind. I just want to get out there.’ Packing herself a small kit back she fled to America under her then agent’s at William Morris Agency and had three weeks in New York, three in LA to try the trans-Atlantic option. ‘I landed off the plane in LA, did a showcase at the Viper Rooms and two days later I’m sat with LA Reid and there are 8 offers on the table. LA said to me he couldn’t believe that British labels had passed up on me.’ Obviously a major talent spots a major talent.

On the last day of a writing session in Hollywood, a song that Jessie scripted with hit-master du jour, Dr Luke, Party in the USA, was optioned by teen-scream heroine Miley Cyrus. ‘To be honest, it was better for her, its way too straight pop for me. The version I wrote and demoed on that day was well ironic.’

First scripted US number one hit under her belt, Jessie J found herself hot property back on home turf. ‘And because I’d been in and out of deals since I was 16, I had the perfect album, exactly as I wanted it to be, ready to go.’

The title track of Who You Are was written in the same week as Party In The USA. As hairs-on-the-back-of-the-neck power ballads and vocal showcases go, they don’t get much better. ‘I was phoning my mum and talking about all these crazy women I’d met in LA who were so different from me. I opened myself right out on that song. I was really down on that day. I was trying to remember who I was before I went out and was surrounded by all these women who looked so Hollywood perfect on the outside. The day I walked into the studio to write it I would’ve rather been in Essex eating pie and mash and watching an old episode of One Foot in The Grave. The words just fell out of me. It was exactly what I wanted to say about myself when I was that lost.’

Outspoken, righteous, cool and fun. There hasn’t been a pop star like Jessie J before. You’re unlikely to find one in the future either. They broke the mould with this one. Is she ready for it all? ‘People sometimes ask me who styled you? Who wrote your songs? I’m like, I did! I’ve got a personality. That’s why I started writing music in the first place. Every single song on the album is a story of my life. I feel ready. Of course I do. I said it on my Twitter this morning. I feel ready, now steady and go are catching up with me.’