Genetically, James Blunt is much too posh to rock. Public school (Harrow), a top university (Bristol), Sandhurst and a commission in the Household Cavalry is not the established career path for an aspiring singer-songwriter. However, his debut album, Back to Bedlam, is a compulsive, gorgeous slow-burner, packed with solid hooks and love songs with a twist, all delivered in the voice of a fallen angel.

Traditionally, rock has been the province of the enlisted man — think Jimi Hendrix and Billy Bragg — but Blunt, 28, is on the march. Radio 2 is championing his album, recorded in LA with Elliott Smith’s producer, Tom Rothrock. He is managed by Twenty-First Artists, which handles Elton John, and signed to Atlantic Records. After supporting Elton live last December, he is now out on the road in his own right.

With his tousled hair, unshaven face and slight frame dressed in motorcycle leathers, Blunt certainly looks the part of the indie rocker. He discovered the electric guitar when he was 14, played and wrote songs, and told everybody he was going to be a musician.

It is hard to imagine him in full Life Guard regalia at the Queen Mother’s lying-in-state, but his family have been soldiers for a thousand years, since King Gorm the Old of Denmark sent his son over to England in the 10th century. “That’s where the term ‘gormless’ comes from,” he grins. “His descendants were very fair. One got the surname Blond, which turned into Blunt along the way.” His father, a colonel, recently retired from the Army Air Corps, and both his grandfathers and all his uncles served. “My father would say otherwise,” he says, in a cut-glass accent, “but I really felt I had no choice but to join the army. I had a naive confidence that I’d get to music along the way.”

Apparently, the modern Household Cavalry is not packed full of drunken hoorays. Some officers painted, some wrote, while others were champions of Amnesty International — and nobody complained when Blunt strapped his guitar to the outside of his Scimitar tank, bringing it out at night to entertain his men with scurrilous songs about senior officers.

After six months in Canada, he was sent to Kosovo as part of the Nato peacekeeping force. He wrote No Bravery in 10 minutes, but whenever he sings it, the scenes he witnessed play inside his head in slow motion. “It’s about meeting Serb soldiers,” he explains reluctantly, “who were standing around reading a porn mag and laughing, smoking a fag over the bodies of Kosovo Albanian families they had just murdered. It was only when someone else turned up that the guilt kicked in.” Blunt is reluctant to debate war further, torn between his inherent, inherited loyalties and his present calling, which has always preferred making love to war.

No Bravery and Cry are exceptions, for in the main he writes clever love songs. The new single, You’re Beautiful, has a melody and a plaintive tone that could make it a staple wedding song. He was inspired by walking past a former girlfriend with her new lover, and making a fleeting eye contact that spoke volumes.

“The core element running through my songs,” he says, “is about the lonely path one walks through life, the connections you make and the thoughts that you don’t generally share with people. I’m a loner, but I’m comfortable with that. I’ve had letters from people, telling me, ‘I split up with my girlfriend, and Goodbye My Lover was the only way I could explain how I felt to her.’ Billy is about my best friend, who owes me a lot of money, and that’s the only way I’m going to make it back.”

The majority of his songs were written in his final year in the Guards. Stationed in London, he made demos and was signed just after he left. His big breakthrough came at Austin’s South by Southwest festival: the American songwriter Linda Perry (Pink, Christina Aguilera) signed him to her label.

While recording the album in LA, James got to enjoy a taste of the rock lifestyle. He was staying with the actress Carrie Fisher, and Goodbye My Lover was recorded in her bathroom. “As you can see, I’ve definitely embraced the way of life,” he jokes. “I take sex, drugs and rock’n’roll incredibly seriously.”

You’re Beautiful is released on May 30; James Blunt is touring until Saturday and plays Glastonbury on June 26