On a poster on a bus stop somewhere near you, the singer Beth Rowley and her corkscrew curls are currently looking menacingly perfect, just above a stack of quotes heralding the 26-year-old as the latest singer-songwriter to be as big as Duffy/Dusty/God. In the flesh though, she's reassuringly scruffy, easy to talk to, quiet even, and she reveals her rather agreeable Bristol roots by answering “yeah man” to any suggestion you might put to her. “I've done some TV interviews and my family are like ‘Beth! All you're saying is yeah yeah, cool cool, that's all you say!' But it's just one of those things. Whatever. Yeah, yeah.”

She is someone you instantly warm to, and what she might lack in repartee, she makes up for with her singing, as she herself is well aware.

“I like really letting it out when I sing because I don't speak very loudly in normal life. The people who are the best singers are not necessarily the biggest personalities. I feel like music is my moment to go and be a show-off; I'm cool not to be in the spotlight the rest of the time. I do feel shy. I read a review the other day that said I looked really nervous - well, I was!

“I'm not somebody who goes on and switches on. And if I've had a bad day, it's hard to fake it.”

Still, her vocals alone were enough to win over the American composer Angelo Badalamenti, the man behind most David Lynch soundtracks, including Twin Peaks. He wrote a song for her to sing on the new Dylan Thomas film, Edge of Love. It is played as the end credits begin to roll, and one of the film's stars, Keira Knightley, has taken a shine to it. “Beth Rowley makes me happy just listening to her,” the actress was quoted as saying. “Yeah, it was in The Sun that Keira liked it, so that was nice, my first Sun snippet!” Rowley giggles.

“It's a period song, it suits the film; not something I'd put on my own album but only because it would confuse things even more because my album is so varied already.”

The album, Little Dreamer, is indeed varied, and went straight into the charts at No 6 when it was released last month, with its solid quota of oak-smoked torch songs. iTunes made Nobody's Fault But Mine its single of the week. This is old-fashioned music with a clean, modern feel, for which the public's ears have been prepared by Mark Ronson's work with Amy Winehouse.

Indeed, the song Oh My Life could be from the Mark Ronson school of Stax-style reworkings, and it has proved a big hit with Radio 2 DJs, being championed by Jonathan Ross, Terry Wogan and Johnnie Walker.

Then there's You Never Called Me Tonight, which is uptempo boudoir blues, and I Shall Be Released is a reworking of Bob Dylan's classic, with an almost reggaeish lilt.

Rowley is a little uncertain as to where her musical direction lies, and admits she has already gone off a couple of tracks on the record. And though her voice is flawless, one imagines it could grow bolder on the next album as she finds her own wings. Perhaps her years as a backing singer have shown her too many options - for, unlike the rest of the recent crop of white soul singers, Rowley hasn't come straight from college. While still at school, she was singing backing vocals for Ronan Keating and Julio Iglesias. She has also sung with Crowded House and the BBC Concert Orchestra.

And then, of course, there's the church. If the album has one recurrent genre, it's gospel - a choice Rowley made because “gospel lyrics tend to be really simple but really effective - like Nobody's Fault But Mine - it's basic form, such a simple song.

“It's a traditional song. I was watching some old Al Green sermons on YouTube and he's so amazing. The sermon itself is like a gig because he's wandering around the congregation and they're all singing out different parts. I went to see him play in London a while ago. It was probably the best gig I've ever seen, I was almost crying.”

The religious angle is relevant. Although her family have lived in the West Country for generations, Rowley was born in Peru, in remote mountains three days away from a hospital, where her parents were missionaries. Her father, a Baptist preacher who wanted to do something a bit more hands-on, moved his family to South America for nine years. They moved back to England when she was 2.

She doesn't remember it and is firmly rooted in Bristol, where the family's outreach work continued. She says growing up with religion was great. “We all got taken to church when we were younger but it was really laid-back, I wasn't forced to go, it was just part of life. People desire to be with other people sometimes. It's nice to go somewhere where it's all right just to sit quietly.”

Did she start singing in church? “Not really ... I didn't really get with that vibe. My music is when I'm out doing my gigs and shouting at the top of my voice, singing the way I want to.”

Her family were musical, though. When not listening to dad's endless James Taylor, Tracy Chapman and Neil Young records, they were out rummaging through jumble sales, hunting down musical instruments.

“We've got shakers, drums and a couple of washboards that we found at those sales. Get the spoon on the old washboard, man, my dad just loves it. And he used to play this old washboard record, Hard Travelling, by Woody Guthrie. I didn't like it at the time but it's so ingrained in me now that if I heard it, I'd probably cry.”

She struggled with her own songwriting until meeting her boyfriend Ben Castle (son of the late Roy Castle), a musician who seemed more fearless than she was. “When I met him he was playing in Carleen Anderson's band at the Jazz Café - she had been my singing teacher - and he needed somebody to sing on some stuff for him. Our relationship just went from there, four or five years ago. He's been really instrumental in helping me with songwriting. I always wrote poems but I didn't know how to hack up the things I'd written to fit round a tune. Singing just came but songwriting didn't. But Ben was amazing. He enjoyed the process - I'd always been scared by it.”

As for playing instruments, she also struggled initially, having tried to sit down and master her Carole King songbook with a guitar. “I'd get so nervous. If I was to practise more I'd get more confident, but I see other people doing it so well ... unless I can do it half decently I'd rather not bother. And Ben has got a piano so I work the tunes out on that, it's easier. And I'm having harmonica lessons!

“Harmonica's wicked, man. You can dive in the deep end and still sound all right if you hit the wrong note. Just hit it with confidence.” Yeah man.

Beth Rowley's album Little Dreamer is out now on Blue Thumb Records. She plays T in the Park, Kinross, on July 13 and Latitude Festival, Suffolk, on July 19

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