Interview: bass-baritone Iain Paterson

Combine this with the sheer number of hours singers spend on stage together for the likes of Götterdämmerung or Die Meistersinger von Nürnberg, and it's little wonder Wagnerians might opt for camaraderie over rivalry.

If Paterson is anything to judge by, his theory couldn't be more spot on. Over the phone he's affable, chatty and unguarded. He lives in deepest Surrey but doesn't sound like it: he grew up in Drumchapel and hasn't lost his Glasgow accent. Both parents were police officers and though neither was a trained musician his dad "had a latent musical talent" and taught himself to play the piano later in life. His maternal grandfather, also a policeman, sang in choirs around Glasgow in the early 20th century. "I guess singing was in my blood somewhere," he says.

Still, Paterson's route into singing wasn't planned. He started playing violin at the age of five and by 12 was leading the orchestra at the High School of Glasgow. He was a multi-talented lad – "a typical Glaswegian teenager who smoked too much and didn't have a clue what I wanted to do when I grew up". He played a lot of rugby and even tried his hand at being a music critic: in 1990 he spent a couple of days work-shadowing Michael Tumelty for this newspaper. Does he recall any lessons from that experience? "I remember it dawning on me that critics are allowed to be supportive as well as negative," he says, without a hint of irony.

In his final year at school Paterson injured himself playing rugby and had to fill up his timetable with either extra maths or a role in the end-of-year show. He signed up to play the role of – who else? – Police Sargent in The Pirates of Penzance. Then when it came time to leave school he applied for university courses but reckoned music college might entail fewer hours in the library. At his audition for the (then) Royal Scottish Academy of Music and Drama he needed a second study as well as violin, and on the back of his Gilbert & Sullivan debut sang a couple of numbers for the panel. He was invited to enrol as a first-study singer on the spot.

From then on it was only a matter of time before Paterson caught the opera bug. He got over his suspicion of libraries when he discovered the RSAMD's record collection, and spent hours listening to recordings of George London and Alexander Kipnis and Nicolai Ghiaurov. It was in that library that he first heard Wagner's Ring cycle, too, but he never imagined he would sing the roles he was discovering. "Hagen, Hans Sachs, Wotan – they seemed unimaginably massive to me. They were the stuff of my idols, not me."

At the end of his second year Paterson surprised himself by winning a college competition and started treating his talent more seriously. Four years in the Opera North chorus after graduating was followed by a move to London and the plunge into freelance life. Then in his early 30s he noticed his voice changing: bulking out in colour and weight and opening up at the top of its range. "I even had a brief dalliance into lower baritone repertoire, but I never pushed my voice in any particular direction. You have to let a voice do what it needs to do."

Clearly the strategy worked, because in 2007 Paterson clinched a role in Das Rhiengold under Sir Simon Rattle at the Salzburg Easter Festival. After that offers flooded in from Opéra de Paris, Bayerische Staatsoper and the Metropolitan Opera in New York. Paterson sings regularly in England, too, at Glyndebourne and English National Opera and Covent Garden, and if his name has been conspicuously absent in Scotland it's not for lack of his own enthusiasm. "I'd love to sing with Scottish Opera – it's my home company, for God's sake! But for some reason my face hasn't seemed to fit for them. I'd also love to see the company turn itself around and put on more than three productions a year. If we're looking down the barrel at an independence vote next year then surely Scottish Opera should be the jewel in the country's cultural crown."

For now, Paterson's thoughts are with Wotan, Wagner's king of the Gods, stirrer of trouble in Valhalla and one of the weightiest operatic sings of all time. He turned down at least five chances to play the role before finally accepting an offer from Huston Grand Opera, which starting next season stages the Ring in one-per-year instalments. "That's how I wanted to learn the role, with enough time to do it properly." But it wasn't to be: in April, after singing a supporting role (Fasolt) under Barenboim in Berlin, Paterson was stopped by the conductor backstage. "I need you to sing Wotan at the Proms this summer," Barenboim asked. "Will you do it?"

With just a couple of weeks to go he's singing the entire role every day, making sure its contours are in his voice and his vocal muscles have the stamina to cope. He says he's well prepared despite the shorter-than-planned gestation period, but readily admits that with a role like Wotan the first performance is bound to be a long way from the finished product. "I turned 40 this year," he says. "It's a good time to be starting this repertoire. Hopefully I'll be singing it for the next 20 years."

Does he take any special precautions to keep his voice in shape? "Not really, I'm bad at that," he laughs. "It's better not to be too precious about these things. Wagner singers aren't particularly more resilient than others, but we probably accept that not every note we sing is going to be perfect.

"A performance of Götterdämmerung usually starts at 4pm; you might catch a cold by final curtain at 10pm. It's like the difference between a 100m sprinter who perfects every movement and a marathon runner who is in it for the long game."

Iain Paterson sings Wotan in Das Rheingold with Daniel Barenboim and the Berlin State Opera at the Proms (Royal Albert Hall, London) on July 22. Live on BBC 2 and BBC Radio 3.