The capitals of the blues are deeply etched in music lore. Every devotee can plot the historical points on the map, from Buddy Guy’s birthplace in Lettsworth, Louisiana, to BB King’s, in Itta Bena, Mississippi. The new name on that roll of honour is a geographical — indeed, a musical — phenomenon: Davy Knowles has reshaped the Delta to include the Isle of Man. History has not previously recorded a bluesman who woke up this mornin’ in Douglas, by the Irish Sea, but Knowles, 22, has emerged from there to stake a credible place on the US circuit, locking down a reputation as a guitar prodigy.

Coming up for Air, his second album with his band Back Door Slam (named for a Robert Cray song), climbed to No 2 on Billboard’s blues chart in the summer. The first-ever production — apart from his own work — by Peter Frampton, himself once a young sensation in a far-off pop incarnation, the record has been rubbing shoulders with Buddy and BB, and younger contemporaries such as Joe Bonamassa and Derek Trucks.

Such renown was achieved by the good old unglamorous means of road miles — hundreds of thousands of them, as the band have played an extraordinary 400 gigs in America in only two years, after Knowles took the opportunity to bed down in the land of his heritage before tackling the UK.

“People in the States go, ‘Where are you from?’ and when you go, ‘The Isle of Man’, they go, ‘Oh, yeah...’” He mimics a faraway, confused look. “Or they assume I’m from London, and I try to explain to people I’m Manx. But it’s a good thing, I think it helps.”

We’re chatting on the band’s tour bus before a gig in San Francisco at Slim’s, the club owned by Boz Scaggs, where Back Door Slam are seizing an opportunity to headline in between shows supporting the rock supergroup Chickenfoot. Any fears that Knowles’s audience would exclusively comprise grizzled greybeards are allayed by the presence of a marked mixture of ages, more than a passing knowledge of his songs, and a noticeably young female contingent. Looks may not have counted much for T-Bone, John Lee or Blind Lemon, but they don’t hurt these days.

Knowles’s robust but honeyed playing and his gravelled vocals are succeeding in selling one of America’s oldest music forms back whence it came. The young guitar-slinger is making the blues sing to teenage American girls, as demonstrated in a message on his blog, on which Krystal, from Indiana, wrote: “I didn’t know who you are, but my father attended Ribfest and saw you perform. You are a great singer, a wonderful artist and...” You get the gist. She goes on, perhaps ambitiously, to invite him to her 16th-birthday cookout.

A self-confessed guitar nerd, Knowles checked out of his local social scene on the Isle of Man to follow his calling. “When I first started listening to blues, it was John Mayall — I got massively into him,” he says, “then Clapton and Cream, then I worked backwards and forwards, into the Delta blues stuff and Chicago scene, and Jonny Lang, Kenny Wayne Shepherd and Stevie Ray Vaughan.

“It was pretty unusual to be into the blues, I guess. But it wasn’t until I started properly gigging that I started getting too obsessed with it for my school friends. I lost a few mates that way, because I didn’t want to go out, I wanted to stay in and play. It never felt like practising, it’s just always fun.”

Latter-day blues musicians sometimes suffer in comparison with their forebears. True, not too many can say that if it weren’t for bad luck, they’d have no luck at all. But do you have to have the blues to play them? “Well, if you’ve had the best life and nothing’s gone wrong for you,” muses Knowles, “you’d be the only person in the bloody world, but there’s no way you could do it. Remember being 10 years old: first girlfriend in the playground dumps you, and it’s the worst thing in the world? That’s the blues, I guess. If that’s the worst thing you’ve been through, it’s the worst thing you’ve been through.”

As it happens, though, it isn’t. As Knowles was finding his way as a musician, the band’s original rhythm guitarist, Brian Garvey, and their mutual close friend Rich Brookes were killed in a car accident.

“We used to see each other every single day,” he says softly. “I was 16, they’d just turned 17. That’s something you never really learn to deal with. It gets a little easier with time, but I still think about them every day. They had the biggest impact on my life.

“That blew the whole school apart, blew the whole island apart. The close-knit group of friends we had kind of crumbled after that, they were the glue that kept that together. I fell back on music in a big way: I’d listen to songs about similar things and I realised, ‘Okay, there’s other people that have been through this.’ But it made me grow up and made me more determined, like, ‘This could all be over, make the most of everything.’”

A fan of the Laurel Canyon singer-songwriter idyll, Knowles includes an imaginative cover of David Crosby’s Almost Cut My Hair in his set, which prompted a treasured e-mail of approval from the venerable walrus. Knowles’s album also includes a version of George Harrison’s Hear Me Lord, another example of his potential to step outside his genre’s expectations.

“There’s definitely an opinion about blues being old man’s music, that you’ve got to be an old black guy sat on your front porch,” he laughs. “When people say, ‘You’re really good for your age,’ you say, ‘Thank you very much,’ but it’s slightly backhanded. I’d rather be really good.”

Coming up for Air is released tomorrow by Blix Street

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