“I never really know what’s good and what’s not,” she says. “I’m just doing what I love, and I’m sure of that.”

Birdy’s self-titled, 1.5m-selling debut album was an extraordinary introduction to an artist who managed to stamp her instantly recognisable identity on all of them. A voice that plugged the listener straight into the emotional mains helped Birdy burrow deep beneath the skin of songs such as The xx’s Shelter, Bon Iver’s Skinny Love and The Postal Service’s The District Sleeps Alone Tonight. Topping the charts in eight countries, the album won rave reviews

Birdy’s new album Fire Within could be described as her second debut, because it sees her stepping into, and shining in, a new role as songwriter-in-chief. Recorded in Los Angeles and London, Fire Within’s 11 tracks include her stirring, propulsive new single, Wings, the tender piano ballad No Angel and Light Me Up, the song that, more than any other, emphasises the dramatic developments in Birdy’s musicianship and writing over the past 18 months. The hushed vulnerability of her first album is there, certainly; nowhere more so than on No Angel and fellow lighters-aloft moments such as Words as Weapons, All About You and Heart of Gold – deeply personal songs that capture Birdy’s incredible ability to convey emotion with the subtlest of vocal and instrumental touches. All You Never Say, meanwhile, combines ricocheting beats with sonorous piano chords, a mix that is at once wintry and warm, as Birdy sings the devastating central refrain: “All you never say is that you love me so.”

I always had strong ideas about how I wanted the new record to sound,” says Birdy, in London to put some finishing touches to the album. “I hadn’t had the chance to explore that before, because my sound was built around just me and the piano. I still love that mix, but being in the studio again and experimenting with all these new sounds was wonderful. The results aren’t dramatically different to how I heard the new songs in my head – and achieving that can be the hardest thing for any artist, so I’m particularly happy about that. Besides, I’ve been writing songs for so long that just to actually hear them on an album feels strange – but wonderful, too.”

Working, as she did on her debut, with the producers Jim Abbiss and Rich Costey, Birdy also collaborated on Fire Within with Ben Lovett (Mumford & Sons, with whom she worked on the song Learn Me Right, from the Pixar movie, Brave), Ryan Tedder, Dan Wilson and Kid Harpoon, among others. Two years ago, she admits, she would have found it hard to articulate her ideas, or to feel confident about trying to do so. “When I first started writing with other people, I was terrified, because on one level, it’s a deeply strange thing to do –go into a room and share your ideas with someone you don’t know. But I love it now, because it’s interesting to hear someone else’s take on what you’ve done, and to draw new inspiration from their ideas.”

Birdy has grown a lot since making her first album. “When I was younger, writing and piano-playing were things I always kept separate, secret, so taking my music out of that separate place was very weird at first. And although I love performing, I get so nervous beforehand. Once I’m playing, though, I go into my own world and then I start to feel more comfortable on the stage.” There are songs on the new album, she continues, laughing, that require her to stand centre stage, rather than tickle the ivories. “I now stand up with a microphone for some of my new songs. It was terrifying at first, but I’ll get used to it.”

Birdy credits her upbringing for helping her to get to where she is now. Growing up on the edge of the New Forest, surrounded by siblings and cousins in a group of houses with the English Channel at the end of the garden, Birdy learnt to cherish the importance of music; her mother is a professional concert pianist, and both her parents have backed her in what she set out to do. “All of my family has the same passion for music and art, so they understand my passion for it.” She completed her GCSEs last year and, despite the pressures placed on her as a touring musician, got the grades she wanted. For now, at least, she has had to abandon her A Levels. “It just became impossible to juggle that with the recording, so I’ve put those on hold. I still see my friends, so it’s okay. And besides, I’m doing what I love.”

And the results? Well, Birdy wouldn’t be Birdy without resorting to a little self-doubt. “I never really know what’s good and what’s not,” she says. “I’m just doing what I love, and I’m sure of that.” Well, we know – and, yes, Fire Within is good. No, it’s more than good; it’s phenomenal.