The word ‘special’ gets used so carelessly that we often no longer hear it, but then every so often something comes along to give it new meaning. Something like Birdy.

In the last six months, more than ten million people have clicked on YouTube to see this 15-year-old from the New Forest perform. It’s hard to believe that such a pure, powerful voice can come from such a tiny frame, or that such raw, deep emotion can be expressed by someone so young. But mostly, what all these new fans recognise is that Birdy is something increasingly rare and precious: a unique new voice, and a musician who can take even a familiar song, and make it all her own.

When her parents fed her as a baby, Jasmine Van den Bogaerde would open her mouth so wide that they called her Birdy. The name stuck – only her school friends call her Jasmine – and she quickly grew into it by making music of her own. She started learning piano at home when she was about seven; within a year, she was sitting at the keyboard making up songs. Her first audience was her extended family: “My mum has ten brothers and sisters, so there are so many of them.”

When she was 12 she uploaded a video of herself performing one of her own songs to YouTube. “Then someone from the record company saw it, and it escalated from there.”

Since then, life has been a bit of a blur. She recorded a demo of her own arrangement of Bon Iver’s Skinny Love, it ended up on Radio One and became her debut single, taking her straight into the top 20 and appearing on TV in The Vampire Diaries. She followed this with an equally original interpretation of The xx’s Shelter, and now her debut album Birdy, with her take on songs by artists such as Cherry Ghost, The National, Phoenix, The Postal Service and James Taylor. “It’s just an introduction to my style,” she explains, saying that doing an album of covers will give her time to finish her GCSEs this year. “Although it’s nice to have one of my songs, Without A Word, on there too.”

Birdy comes from a talented, creative family (her great-uncle was the actor and writer Sir Dirk Bogarde, although Birdy is too young to have ever met him). They live in a crumbling converted mill in the New Forest, not far from the sea. There’s a grand piano in the living room because her mum is a classically trained concert pianist. In a shed outside, there’s the tiny studio where Birdy recorded some of her first demos, and where her dad works, recording voiceovers and reading the day’s news stories for the blind. With her younger brother and sister, a whole pack of cousins living close by as well as her friends, Birdy has had a childhood straight out of an Enid Blyton book: roaming through the woods, and playing on the local beaches.

There’s a reservoir just outside that the family uses as their open-air swimming pool, a little dog and a huge, tiger-like cat that’s big enough to catch rabbits. There’s a wasps nest above her bedroom that may or may not get removed in the next few months, and a bees nest in the outer wall that would be harder to get rid of, because it’s been there so long now it’s hard to tell what is honeycomb, and what is wall. “All night long I can hear them buzzing,” she smiles. “I used to hate it, but now I’ve got used to it. It’s quite nice – it lulls me to sleep.”

More recently, she sang in a band formed by her older brother, Moses, who lives in Brighton. “We would go to pubs in London or Brighton, and after we’d played, they’d say that I had to leave immediately because I was too young to be in there. So I’d have to wait outside, and different band members would take it in turns to like babysit me. So they’d all be inside having fun, and I’d be outside. It was funny!”

She turns 16 next May. She is starting out with an album of covers partly to take the pressure off and give her time to develop as a songwriter, but mainly to give her time to finish her GCSEs this year.

“It’s just an introduction to my style,” she explains. All were arranged by Birdy and performed in her own way. “I’d listen to them, then decide which ones I’d try out. Usually I just sit at the piano and work out a part that feels like it’s my style, then I’ll work with the voice properly. And from that, I’d choose which ones I thought would be good for the album.”

Her sound is so uniquely her own that it’s hard to talk about influences. Critics have likened her to Kate Bush, but she likes listening to Lykke Li, Paolo Nutini and Adele, whose reserved performing style she particularly admires. But her biggest influence is her mum, Sophie. “I’ve listened to her playing the piano all my life. And I love that.”

The first demo vocals were usually recorded in the shed at home on her dad’s computer, or even on her iPhone in her bedroom, and the recordings were completed in London and Los Angeles on weekends and in the school summer holidays with some of the hottest producers of the moment such as Rich Costey (Muse, TV on the Radio), James Ford (Arctic Monkeys, Last Shadow Puppets and Klaxons) and Jim Abbiss (Adele, Arctic Monkeys). “They’ve been so supportive, giving me ideas and telling me what sounds better than other things, but I’ve had a lot of input.”

When she was due to perform on Radio 1’s Live Lounge, for instance, she decided at the last minute to change from the track she’s been rehearsing to perform a spine-tingling version of Ed Sheeran’s The A Team. Her instincts were proved right: with over 400,000 viewings, it made her the second most viewed UK artist on YouTube.

She’s already talking about her second album, about the songs she’s written herself and can’t wait to record. “I’ve had loads for ages, but they’re not finished. They’re just sketches of songs that I have in my head. I can’t wait to start putting them together, and see what people think of them.”

This is her dream, she says, the thing she feels she was always meant to do. Although the reality doesn’t quite match up to her fantasies. “You have to actually put in the work as well, to get a good outcome,” she smiles. “It doesn’t all just come to you. I don’t think I ever thought about that bit! I just thought about the perks of fame – I imagined going to glamorous parties, and having a limo to take you everywhere. So far, I haven’t had one!"

Birdy is a beguiling mix of contradictions: she’s young, yet sings in a voice that is world-weary and steeped in soul. She’s shy and nervous, yet once she steps onstage, she’s an astonishingly focussed and charismatic live performer. She’s fragile, yet strong enough to fight her corner with both producers and label when she needs to. She is, quite simply, unique. And this is a story that has just begun.