She didn't get to go home again until she'd recorded debut album Eye To The Telescope. Wowed the nation with her one-woman blues-stomp 'Black Horse And The Cherry Tree' on Later... With Jools Holland. Toured the world a fair few times. Become a festival favourite from Glastonbury to T In The Park (and back again). Secured a Mercury Music Prize nomination. Outsold every other female artist in the UK in 2005 (bye bye Madonna, see ya Mariah). Won a Brit Award for Best British Female Solo Artist.

Won the Ivor Novello Best Song award for writing Suddenly I See. And a Q award for Track of the Year for Black Horse and the Cherry Tree. Landed a Grammy nomination for Best Female Pop Vocal Performance. Lent her tunes to choice American films and TV shows (eg, Suddenly I See, used in the opening scene of Meryl Streep flick 'The Devil Wears Prada'). Watched her songs become staple audition material for contestants on American Idol. Found time (OK, it took a day and a half) to record and film her lo-fi 'living room' album, Acoustic Extravaganza, live with her band on the Isle of Skye. Signed up for the GlobalCool campaign, which took her to Tony Blair's house in attempts to put pressure on the government to reduce carbon emissions. Sold almost four million copies of Eye To The Telescope, including over 1.5 million in the UK alone and over 1 million in America.

'The last three years have changed me as an artist,' says the 31-year-old Scotswoman known to her family as Kate. 'I don't think it's altered me as a person. Which is a relief! I think the major part of that change is that my bar has been raised - I've realised what's possible throughout the last three years of making a first album, touring it with a band, seeing how that album can turn into something else on stage, and how we can actually make it better. And that it's imperative to improvise.'"It's always been about getting onstage and trying to do a mindblowing show."In those years Tunstall had become, at least in part, that elusive music business holy grail: a word-of-mouth phenomenon. Commercial success though, as Tunstall is all too aware, can also have its pitfalls.

'You can allow it to become a bit of an albatross if you're not careful - where you think you have to just go out and slavishly recreate what people liked. I heard a theory that you cease to mentally progress from the age at which you become famous! It's easy to be frightened to move on and change what you do. But because I've never really been a studio artist, that's just never really applied. It's always been about getting onstage and trying to do a mindblowing show. And if you're playing the same set night after night, that means playing around with it, you know, and experimenting with what you've got. It's not a cd, it's a gig.'

Then, after all that - the tours, the awards, the nightly mixing-it-up, KT Tunstall got to go home and put her feet up. For five minutes. She'd been working on, and with, and for, the tunes on Eye To The Telescope for so long that there was a backlog of new songs needing some attention. And if you'd worked as hard and as long as Tunstall had to secure a record deal in the first place, you wouldn't hang about either. It was time to work on her second album, a collection of thumping pop songs and intimate, oftern mysterious ballads that she's called Drastic Fantastic - a title that popped into her head as she was writing her journal on an aeroplane.

'I'd been blown away by the film 'Sin City', and I'd loved how Frank Miller's imagery came to life. It made me think, doing this for a living is such a comic-book existence. It's a bit like the X-Men minus the actual super powers! You're flying everywhere, you're on stage, you're euphoric, you're down, you're thrown around, you're exhausted to the point where you can't stand up or speak. That's abnormal! Drastic Fantastic sounded like the name of my comic-book life.'

"I remember a brilliant game we'd play in the evening when the lights were dimmed. Dad would take a big canister of liquid nitrogen and sloosh it down the linoleum corridor."KT Tunstall knows a lot about peculiar journeys. She grew up in Fife on Scotland's east coast, the daughter of a primary school teacher and a physicist. It was her childhood trips to the St Andrews University Observatory with her Father that, years later, gave the first album its name. Her physicist father also provided an imaginative environment, often letting her spend time in his laboratory.

'I remember a brilliant game we'd play in the evening when the lights were dimmed. Dad would take a big canister of liquid nitrogen and sloosh it down the linoleum corridor. Me and my bigbrother would sit huddled together on the canister trolley, dad would say "don't touch! Your fingers'll fall off!" and he'd give us a wee push and we'd sail through low level clouds, watching hundreds of little bubbles bounce off each other.'

The family would often take off to go camping or hillwalking, regularly driving to France, and consequently a young Tunstall was instilled with a deep-rooted attachment to landscape and travel. It was an isolated yet vibrant small - town childhood. There wasn't much music in the Tunstall household, nor much telly - her younger brother is deaf and having the tape-player or TV on made it even more difficult for him to join in conversations.

But Tunstall found her creative spirit at a young age, joining a local grass-roots theatre club and taking lessons in dance and various musical instruments. 'Performing always felt right; like an electrical circuit being completed and the lights coming on'. Tunstall thinks that the lack of music in her childhood 'stopped me being cornered by anything. If your parents only listen to jazz or folk or something, you're like one of those trees you see in botanic gardens that have wire frames on them - you grow into that shape, you follow it or you have to break away from it. But I didn't have influences to embrace or kick against - I also had no idea what anything was. The whole idea of certain types of music being cool is a relatively new idea to me.'

From famine to feast... Aged 16, Tunstall fell in with, and fell in love with, a bunch of Fife musicians. Over the next few years she learnt all about folk music, living in cottages, scraping a living, signing on, eating stolen turnips from neighbouring fields, keeping warm by strumming acoustic guitar extra vigorously. Those musicians became the Fence Collective, nominally led by Kenny Anderson. Now known as well-regarded singer-songwriter King Creosote, Anderson was something of a mentor to Tunstall.

'It was a very formative time for me. Eyes and heart wide open. I learnt about being a musician; not trying to be rich and famous, just about being a musician.' Those years also saw her journey to and fro to America to study for a year, but 'mostly to play and travel'. After Fife, Tunstall's musical journey took her to Edinburgh, where she busked and hosted her own acoustic nights, Acoustic Extravaganza, which gave the Skye album its name and is still put on by friends under the name Acoustic Edinburgh. Finally, after deciding opportunities may be passing her by and with the promise of a publishing deal, she begrudgingly moved to London.

That said, Tunstall thinks that London has 'seeped under the door' of Drastic Fantastic, and is glad of it. During the making of Eye To The Telescope she was listening to a lot of Sixties singer-songwriters. This time round, she was listening to the radio, mainly the pop-indie output of London's XFM. The White Stripes, Arcade Fire, The Killers, Bloc Party, as well as all those months touring, have resulted in a hardening, if you like, or a quickening of Tunstall's playing and writing - I Don't Want You Now is a jump-around pop gem, destined to be a huge, hands-in-the-air live favourite. 'Kirsty MacColl doing Teenage Kicks,' as Tunstall describes it with a grin. 'I definitely found my little inner folk-punk on that one'.

Her adopted hometown is also there in the album's first single. Hold On is a thumping great hoedown, as infectious as any of Eye To The Telescope's still-ubiquitous brace of hit singles. Underneath the resonant twang of her beloved Gretsch Falcon semi-acoustic fed through a 'really nasty amp', Tunstall has laid a big fat, ferocious beat.

'It was actually born out of this dancehall beat that soaks Harlesden. Every single car is just pumping dancehall out the windows, and I love it. And it sort of feels like I can play around with it now cause I've been around it for long enough.' It took Tunstall and Steve Osborne - the legendary producer with whom she's enjoyed a hugely productive and collaborative relationship on both her studio albums - five months to fix the tune: 'We had to get it right or it could have ended up sounding like the Gypsy Kings or cheesy R&B! The inspiration for the lyrics - "hold on to what you've been given lately/because the world will turn if you're ready or not" - was Bob Marley's 'Judge Not'.

'I'm saying, "don't waste your time pointing at me, look at what you do, look at how you are, maybe you want to spend less time giving me .shit" It was about an old relationship I was in. It's always empowering when you come out of something difficult, to keep the parts that have actually taken you somewhere else and moved you on rather than that stuff that's made you feel low about yourself. That's very me. I'm always looking for the shaft of light in a bad situation.' Drastic Fantastic is an album brim-full of powerful lyrics, bold, colourful melodies and the increasingly adventurous musicianship of Tunstall.

'I wanted to be braver,' she says of the mindset and purpose behind Drastic Fantastic. "It's like The Prophet by Kahlil Gibran - that's a beautiful book, and there's a bit where he talks about your heart being like a well. If you have a shallow well, it's always really easy to get the water out of it, but you can never fill it with very much water. And the deeper you dig, the darker it gets, the colder it gets, and the emptier it feels when it's empty. But when it's full, its proper chocka! And it lasts! And I really believe in that.' 'I also wanted to push the musicality on the album,' she continues. 'I really enjoyed playing lead guitar for the first time, as well as piano, Rhodes, ukelele. But also: I felt my vocals were a little safe at times on the first album. I didn't mean that to happen but I was so inexperienced singing in a studio that I couldn't quite get my live voice into the booth. After three years of touring you get so good at just flipping yourself into gig mode; finding whatever underground stream it is inside that provides you with that magical lucidity. I found that now I can tap into that really quickly. And for the first time, being in the studio was another stage.' Other highlights on the record? 'Saving My Face', 'about 50-year-old women trying to look like teenagers' - Tunstall is looking forward to making a video for the rollicking tune, 'something involving plastic surgery, like those before and after tv programmes! They're so compelling.' 'Someday Soon', a quiet, delicate jazz-inflected song, Tunstall's voice fluttering from whisper to hearfelt cry with ease. And perhaps most ambitious of all, 'Beauty Of Uncertainty'.

The latter is a close-up ballad and the longest song on the record, Tunstall singing in hushed intimacy over delicate picking, with an ending as wide as a canyon. It's named after an essay by Canadian writer Brian Hendricks. Tunstall borrowed an excerpt for the sleeve of Acoustic Extravaganza. Now she and Hendricks have written a screenplay based on the essay, with Tunstall - on and off-page - playing the role of muse to a burnt-out director. Indeed, she sings the song as the character, 'Sweet Jane'. Conceptual album artwork (wonders of which to be fully explained later on Tunstall's website), will be as carbon neutral as possible and appear on 100 per cent recycled paper. To that end Tunstall's London home is also undergoing an eco-transformation - her new studio and loft extension won't be made of second hand paper, but will use reclaimed wood, sheep's wool wall insulation, spray taps and solar panels.

It all fits in with a serious, ongoing, deep-rooted commitment to green issues: Tunstall's tour buses run on bio-fuel, she's a fan - and wearer - of eco-fashion, she doesn't own a car, and she's a prominent supporter of the LiveEarth concerts, appearing on the American line-up at Giants' Stadium in New Jersey. Her 6,000-strong forest of trees in Scotland was planted as the copies of her first album left the stores.

But at the heart of all this is Drastic Fantastic. An album rich in beautiful songwriting and beautiful sentiment. An album made in scruffy, comfy environments but that sounds rich, deep and intimate. An album to go round the world but that won't cost the earth.