Unless I specifically inform you otherwise (to paraphrase that great line in Martin Amis’s Money), James Rhodes is smoking. And swearing. And gesticulating wildly. We are basking in late afternoon sunshine on the balcony of the Royal Festival Hall, the Thames spread spectacularly before us, and the punters gathering for the evening’s concert aren’t paying much attention. Still, as he stresses how much “I fucking love Rachmaninov”, I’m suddenly glad I didn’t suggest the genteel surroundings of the Wigmore Hall.

Rhodes, 35, hasn’t been dubbed “the pianist with the rock star attitude” for nothing – in promo shots he looks Dylanesque and today he’s waif-like in black drainpipes, a novelty T-shirt, straggly hair and geek-glasses. But this image masks a strong commitment to traditional repertoire. “I’ve always been full-on core-classical,” he says. “I don’t see the point of crossover, it seems to suggest that the average person is too stupid to deal with a whole Beethoven sonata.” Last year’s debut recording, Razor Blades, Little Pills and Big Pianos, may be explicit in its autobiographical reference (more on that anon) and achingly stylish, but it’s a serious recital disc with a Bach French Suite at its heart.

Rhodes had no formal training but, armed with a passion for the piano bordering on obsession, he has made it his mission “to open up a dialogue between performer and audience”. I’ll admit to some scepticism (an endorsement from the ubiquitous Stephen Fry did nothing to allay my fears) but his gig the night before at the Southbank’s Udderbelly tent, while far from definitive, was thrillingly communicative, with blazing interpretations of Beethoven’s Waldstein sonata and the Bach-Busoni Toccata, Adagio and Fugue in C major interspersed with witty introductions. Rhodes might lack the technical skill of conservatoire students, some trills were blurred and notes fudged, but he makes no apology...

An “insanely enthusiastic” piano student at school, Rhodes dropped out of a music degree to study psychology and ended up in a City job. After six years of “money and mania”, he says, “I’d resigned myself to the fact that I wasn’t going to be a concert pianist so I thought I’ll become an agent instead, then I can surround myself with the great classical artists and live life vicariously through them. Like going out with Cheryl Cole’s uglier sister,” he laughs. So he sent a case of Krug to Franco Panozzo, agent to the great Grigory Sokolov, and was finally invited to meet him in Verona to discuss each throwing €30,000 into establishing a London office.

When, on a whim, Panozzo invited him to play something on his Yamaha grand, Rhodes did his best with a Chopin étude. “I turned around afterwards and he just sat there with his jaw on the floor,” he explains, “and he was so sweet, he said ‘You’re not going to be an agent, you’re going to come to Verona every month for four days, you’re going to study with my friend Edoardo Strabbioli, the finest teacher in Europe, and you’re going to become a pianist’.” This wasn’t the end of his troubles – illness returned and resulted in a spell in psychiatric hospital – but gradually he began his ascent....

yet the musical interpretation is autobiographical already and I want the whole thing to feel personal. That’s why I talk at concerts, I don’t think audiences necessarily want to read about sonata form but I imagine a lot of them want to know that Beethoven was almost beaten to death as a kid, twice, by his alcoholic father.”

It’s this everyman attitude that has recently charmed Warner Bros into signing Rhodes, alongside the likes of Madonna and the Red Hot Chilli Peppers, as their first classical artist. Work has already started on the first of a contracted six albums for the label, but in the meantime like any self-respecting pop artist Rhodes is working the festivals. Last night he played at Hay-on-Wye and next month he has slots at Cheltenham and Latitude