Standing stock-still in the basement of an instrument shop, clutching a tiny pink guitar, Birdy looks even younger than her years (17) and smaller than her height (5ft nothing).

The classically trained singer/songwriter might be in her comfort zone surrounded by musical kit here in central London’s Denmark Street for the benefit of the New Review cameras. But the girl born Jasmine van den Bogaerde is also far from home: her extended family’s 1,500-acre estate in the New Forest.

Given her background – countryside, quietude, daughter of a concert pianist, great-niece of Dirk Bogarde – Birdy’s shy, well-spoken, super-polite reserve is understandable. But she’s unlike what we think we know of most modern teens in other ways, too. Put her on a stage, as did the London 2012 Paralympics Opening Ceremony artistic directors, and Birdy and her voice and piano can light up a stadium (she sang Antony and the Johnsons’ “Bird Gerhl”). Give her a songwriting brief, as animation company Pixar did for the Scottish-set Brave, and she’ll compose a stirring, Celtic-flavoured folk number (“Learn Me Right”, made in collaboration with Mumford & Sons). Inspire her, as she was by reading (in one week) the Hunger Games trilogy, and Birdy will write a song and submit it, on spec, to the film-makers – Hollywood studio Lionsgate promptly used “Just a Game” over the closing credits of last year’s $700m-grossing blockbuster.

Those opportunities all flowed from the international success of Birdy’s first album. Released in late 2011, her self-titled debut is a collection of gossamer-light but emotively strong, piano-based covers (and one original). The lead single, an English adolescent’s take on Bon Iver’s “Skinny Love”, gave Birdy a Top 20 hit when she was aged just 14, while her versions of songs by The xx, Fleet Foxes and Phoenix were classically framed, savvily chosen reimaginings of cool tunes by hipster bands. To date, the album has sold almost 1.3 million copies worldwide.

Now comes the next phase of the careful, well-thought-out promotion of Birdy: an album of new, co-written songs. On Fire Within, the girl who gained her nickname in infancy (she ate food like a chick, seemingly) has both broadened her sound – ringing guitars, thumping drums, belting choruses – and her songwriting palette. In studios in Los Angeles, Denver, New York and London, Birdy has worked with some of the best writers in the business: Dan Wilson (Adele’s “Someone Like You”), Ryan Tedder (Leona Lewis’s “Bleeding Love”), Ben Lovett (of Mumford & Sons) and Kid Harpoon (Florence & The Machine’s “Shake it Out”).

To her credit, Birdy admits that she was initially resistant to writing with top-drawer hitmakers-for-hire. “I wanted to do it all myself,” she says in the whisper-like speaking voice that’s in sharp contrast to her strong, resonant singing voice. “I was so used to writing on my own at the piano that it just seemed weird, going into a room and meeting someone for the first time and opening up and giving them all your ideas. It just felt kind of embarrassing.”

Plus, the kid discovered in 2008 by her record label via a low-key talent show, Open Mic UK – and who signed a publishing deal aged 12 – had a clear-sighted, simple goal: she wanted to make music in a manner that felt, well, proper.

“I was scared that it was almost like cheating,” she says of her various writing sessions. “But actually you’re giving so much, and you’re both aware of each other’s ideas, and listening to each other. It’s not like one person is taking over. You’re sharing, and I loved that.”

Not surprisingly, the beautiful, atmospheric and punchily melodic Fire Within has elements of the best of her co-writers’ previous clients – but rounded out by Birdy’s undeniable writing skills and topped off with her richly expressive voice.

Right now, two weeks shy of the album’s release, Birdy is deep in rehearsals with her band in Bath upfront of the international touring commitments that will stretch well into next year. “Last time I was always hiding behind the piano,” she admits with a nervous laugh. This time she’ll be playing guitar and – more worryingly for a girl who is as far from the X Factor school of performing showpony as you can imagine – standing up at the microphone.

“I should probably get some lessons in stagecraft. Cos I can’t dance – I think I have rhythm but I just don’t look right,” admits the teenager. “I might have to work on some hand movements. That’s one of the reasons I like Adele – she doesn’t have to do much [on stage] but she’s still strong, and she’s amazing to watch.”

Meanwhile, her band of twentysomething musicians are introducing her to “old films” (recently watched faves: Top Gun and The Breakfast Club) while, in advance of a European tour, Birdy herself is gently extricating herself from the parental yoke. “My parents don’t come as much any more, unless it’s far – they came to Australia,” she says, neglecting to mention that her trip Down Under was to play three sold-out shows at the Sydney Opera House. “But my band are a wonderful team and I feel safe. I don’t need my parents as much any more anyway.”

Does she have any plans yet for her 18th birthday? “That’s next May, and I might be in America. But I’d hate to be in America then cos then you have to be 21 to go to loads of places and to have a drink. So hopefully I’ll be in Europe. I like beer, and I like wine. But I don’t like anything sweet, so I can’t drink spirits. Well, vodka’s OK, but vodka and Coke is pretty nasty,” she says with an expression that says “eww”.

So, it’s in with old-fashioned songwriting and performance integrity, and out with youthful excess for this quiet girl who is still mortified at having to tweet to her quarter-of-a-million followers. But what else can Birdy tell us about the modern teenager?

Birdy on…

Justin Bieber

“Me and my sister, who’s 14, listen to him. He’s a bit of guilty pleasure. It’s something all my friends listen to – it’s party music. It’s not something I’d listen to if I was on my own; I wouldn’t put it on my iPod. But I do like it – it’s fun! You can hear that he’s musical. I remember watching those first videos on YouTube, and you could see then that he can sing and he can play.”

…Ed Sheeran

“I was quite starstruck when I met him. He works so hard and puts all his energy into what he does. I love that. And he’s a brilliant writer. He’s someone I look up to.”

…One Direction

“I like their music – again all my friends are listening to them. We were playing at the same awards show in France and their energy is amazing on stage. I got to meet Harry Styles the same time I met Ed Sheeran, at the Little Noise [charity] gigs in Hackney in London. He was really, really sweet. Could I see the attraction? Yeah, definitely! He’s really good-looking. But my friends don’t love him necessarily – they probably just love all of them.”

…juggling pop and exams

“I got my GCSE results last summer, and they were OK. Music I got an A, maths I got a B, English I got an A and a B. There was only one C, which was drama, because I just didn’t do the writing part, which was a bit silly. You had to do lots of 2,000-word essays on lots of different plays and stuff. I just didn’t get round to finishing it in time. But I was really pleased with the other results – I thought it was going to be awful.”

…putting her A-levels on hold

“I started A-level French and Art but I left college earlier this year. It was my parents who were like, just focus on one thing. And the college was really amazing. They just said that if I want to come back, I can. They knew music is what I love doing, and cos I was trying to do both, I was hardly ever at college. So they understood it was better if I was giving my full concentration to music or studies.”

…TV talent shows

“I’d love to sing on The X Factor! I love those shows. They can be a good platform for young artists, but it depends on what kind of person you are. It wouldn’t have been right for me – I needed things to happen gradually. Being in the public eye so quickly, I think I would have freaked out about that. You have to be ready and I wasn’t. Also, a lot of the time it’s not about the music. That’s another reason I would never have gone for something like that. But some people like that…”

…cyberbullying

“I’ve not had it so much on Twitter, but you see nasty comments sometimes on YouTube. It’s just important to keep away from it; there’s always going to be people who don’t like what you do. Constructive criticism is good, and I take all of that on board. But just hate is nasty. If you get some horrible comments, it’s important not to keep going back to it – cos that’s when it can get nasty. But it does happen, and you shouldn’t take it seriously – and it’s important to talk about it with your friends. You shouldn’t just keep things like that to yourself. That’s when it becomes more of a problem.”

…social media

“Twitter is how my friends communicate. I still read their stuff, but I’m more of an observer. But definitely all my friends use Twitter and Facebook – it is a huge part of being young. If someone was having a party, it would be on Facebook. And we all keep in touch via Facebook – that is amazing having it just to talk to them. It’s nice to be updated with what everyone’s doing. It brings you back to home and what’s going on there. I’m always quite careful about what I post. But I don’t think a lot of them are. Your digital footprint? Most people don’t think about that.”

…not having to wear braces any more

“Yesss! That was really nice. I only had them for a year-and-a-half – I was lucky. There was no point hiding them, and everyone knew, so I used to post pictures of the new colours every time I went to the orthodontist – ‘Got green today, Christmas colours!’ I definitely felt self- conscious, though, especially when doing photos. When I got press pictures done, I used to keep my mouth shut. That’s probably some of the reason I look quite grumpy in a lot of the early photos – ‘Don’t show the braces!’ The worst food to eat was sandwiches. That was really bad. Not nice. But just any food, really.”

…boyfriends

“I don’t have one. I just have to meet the right person. It’s quite easy to tell if someone’s interested in me as a singer rather than a person. It’s something I’m aware of and I can see it coming. But it’s not my focus at the moment – it’d just be a bit unfair cos I’m so busy. It’s not time.”

…being a globe-trotting teenager

“I miss the events and things that are happening at home, and being away always missing them. But I do get to go home quite a lot – I’m really lucky, and I get to join in when I can. So I’ve got the best of both worlds, which is amazing. And I didn’t get any bitchiness. I’m close with all of my friends, and we all kind of moved from school to college together, so I knew all of them. So they’ve just been great. And I’m doing what I love, so I’m really lucky.” 1

‘Fire Within’ is out on 23 September