Bryn Terfel: 'I haven't been pushed to the limit yet'

'Good!" booms Bryn Terfel. "They got the Rolex!" In a couple of minutes spent flicking through 30 or so new publicity shots, it's pretty much the only comment he has made. To smouldering poses of him on beaches, or hillsides, or standing with a blonde, or pulling a massive rope, his only response has been "fine, fine". Where anyone else might be poring anxiously over every wrinkle, every bulge – where a journalist, for example, might be begging the picture editor just to soften those under-eye shadows the teensiest little bit – this bearded giant of a man is merely glancing and nodding. This, clearly, is a man without narcissism. This, clearly, is a man at ease in his own skin.

In his hippyish shirt, khaki jacket and trousers, and tweed cap, he looks like a gargantuan morris dancer, or perhaps an extra from Sir Gawain and the Green Knight. But when he opens his mouth, it's like being dipped in the darkest, most expensive chocolate you can buy, and being rolled around in it, and doused in whisky. A voice like that, you can't help thinking, might have saved those bankers in that grilling last week. A voice like that might have had the nation purring.

And when the giant morris dancer sits down opposite me, in an "interview room" at the Royal Opera House so tiny that our knees are almost touching, I realise that it's not just the voice. This man, who bears a passing resemblance to John Goodman in The Flintstones, has a gaze that bores into your soul, a gaze that is, quite simply, magnetic. In this space the size of a car, the combination of both – the voice, the gaze, the presence, in fact, that fills the world's largest opera houses and sends hundreds home weeping – is almost overwhelming. It has me fumbling with my tape recorder. "Er yes," I say, when we do a quick soundcheck and the voice of God booms back at me. "Er yes, that's fine."

Bryn Terfel is in the middle of rehearsals for Der fliegende Holländer (The Flying Dutchman), which opens at the Royal Opera House next week. It's his first run here for a while. He was due to play Wotan in The Ring in 2007, but pulled out to help his son through surgery on a broken finger, a decision which created what passes, in the opera world, for a storm. But I don't want any storms unleashed from two feet away, so I don't mention it. Instead, I babble on about how intimidating the world of opera can seem to those not in it.

The world's greatest living bass-baritone gives me a gentle smile. "We do live in another world," he says kindly, "when we're on the stage. When we open the door to the opera house, I think we become different creatures. We're all different, you know?"

Well, yes, I wasn't really thinking of the singers on the stage, actually. I was thinking more about the audience, and the rituals and the clothes and the critics and the, er, prices, but I let that pass. "Angela Gheorghiu, for example," he continues, "when she comes into the opera house, she is a different personality to when she is outside."

And, by all accounts, a rather trickier one, but that's not an accusation (before the broken finger incident, at least) ever hurled at Bryn Terfel. "I want to work hard to be as colleagual as possible," he says, "but when the bell rings I'm ready to work and achieve something on the stage because we have a contract to fulfil. I know that sounds a little bit clinical, but in essence that's what we have to do. Because people are spending their hard-earned money to come and see us, hear us perform, so the least we can do is be regimental – you know, homework done."

He has, in fact, already done his homework on this role. He played the Dutchman in David Pountney's production of The Flying Dutchman at Welsh National Opera in 2006, The production was set in a Kazakh space-station, and attracted – well, let's just say, an awful of controversy. Terfel's singing, however, wasn't faulted.

"You take a story that is all to do with the sea," he says circumspectly, "and you go to space, then you are going to be out for criticism. But I had friends who'd never been to a live opera and loved the experience anyway. The music was enough of a vehicle for their enjoyment. Controversial or not, we still have to come up with the goods." Indeed. And how does he prepare? Not just the singing, but getting into the role? "You can't turn up and expect to do the same performance every time," he explains.

"I've got a score that I was given by the widow of a very famous opera singer from America called George London. He had written down on his score exactly the sort of problems that I have with it. Breathing, difficult phrases, climactic bars within certain scenes. I'm in the same boat as every performer who's attempted to perform this piece."

Bryn Terfel, it's clear, has a tendency to talk as though he were assembling Ikea furniture. Some of it's tricky, at first (those Billy bookcases can be deceptive) and everyone struggles a bit, but with a bit of effort you get there in the end. He doesn't, in other words, talk as if the sound emanating from that too, too solid chest is one that has critics fainting with delight, be-taffeta-ed ladies shrieking orgasmic approval, legions of fans flying to see him round the world. He doesn't talk as if his Wotan, for example, in Keith Warner's production of The Ring, had been greeted as if it had been wrenched from heaven and hell, greeted as if it were the voice of God.

He admits that he finds the prospect of Die Meistersinger von Nürnberg, which he'll do at Welsh National Opera next year, "daunting", but unlike the opera critics, doesn't see his career in terms of pinnacles or peaks.

"I think the most important opera that I ever sung," he says matter-of-factly, "was the very first I did. It's like going from being a trainee footballer to being a professional one, to then going into management and finally deciding that that's enough, the denouement is at hand."

Unlike opera critics, too, he is as happy singing folk songs or songs from musicals as arias from Wagner or Schubert lieder, and he's as happy working with Ronan Keating and Sharon Corr as with the opera greats. With international opera bookings (sons' fingers allowing) firmly inked in until 2013, and then maybe that "denouement", he has just taken a year off from opera.

"It was," he says, "brilliant. It meant I could choose which concerts I wanted to do. I sometimes arrange them around sporting activities like the Ryder Cup. I went to see Calzaghe in Las Vegas. In a way, it's as if you are just going back to the beginning of your career. You start, really, through concerts and operatic experiences take over."

By "you", of course, Terfel means "I". Unlike most megastars – his CDs sell literally millions – he's not that keen on the one-letter personal pronoun. And how he started, really, wasn't through concerts, but home and church. Born in rural North Wales in 1965, the son of a sheep farmer and a special-needs teacher, he grew up with music all around. "My parents sang," he says, "and my grandparents sang, but sport was the most important thing in my life." He was thinking vaguely of becoming a fireman when a teacher complimented him on his voice and suggested he go for an audition. Keen on the idea of a couple of days off school, Terfel learned two songs and a Dylan Thomas poem and set off for the Guildhall School of Music. "They gave me a scholarship," says Terfel, with another flash of that mesmerising smile, "which in Wales is a big word."

Helped through serious homesickness by two fellow students (one now a music teacher and the other an armed police escort), he went on to win the Guildhall's Gold Medal. In 1990, he made his operatic debut as Guglielmo in Cosi Fan Tutte at the Welsh National Opera. The following year, he performed at English National Opera in London, Théâtre de la Monnaie in Brussels and Santa Fe Opera in the US.

For years, he travelled nearly all the time, returning between roles to his home, just a few valleys away from where he was born, as was his wife, Lesley, who he met at primary school. "As a young singer," he says, "you take on everything because you think you will never have another job." It isn't, I tell him unnecessarily, exactly common for an international opera star to live in the community where they grew up, to spend Saturday nights with the people they went to school with and to remain married to their childhood sweetheart. Is it?

"I could name you 10 immediately!" he says. "Our lives have changed, of course," he continues levelly, "but I think the benefits far outweigh what negatives there are. You meet some wonderful people and some wonderful people that love what you are part of. And I've started a festival. It means I have to be here in the summer."

Ah yes, the annual Faenol Festival, in a field near his home, which has brought together Jose Carreras and Shirley Bassey and Jamie Cullum and Andrea Boccelli. A festival, in other words, which brings together the highbrow and the lowbrow and the middlebrow, a festival that's all about pleasure, not snobbery, a festival that's the festival equivalent of Bryn Terfel.

It's a mystery, actually, that this bloke-ish, extraordinarily good-natured man, happily married, with healthy children and still-living parents he adores, still deeply rooted in a community he loves, and pursuing a career that also happens to be his passion, can produce a sound that makes your soul tremble, a sound that feels as though it has tapped into the deepest anguish of the human heart. So, where does it come from, this angst, this passion? And is he really as sunny as he seems?

"Well," says Bryn Terfel, and he might be talking about what he had for breakfast. "It is a Welsh trait, in a way, to sweep things under the carpet and want an easy, happy life. Yes," he says, "I think I am."

With his family and his work, his friends and the sport he loves as much as music ("don't make me choose!"), Bryn Terfel seems that creature rarer than a humble banker, an artist who's happy. He wants to retire to a golfing community. He's always nice to his fans. And he's always calm. Isn't he? "I think," he says, and perhaps I can glimpse a shadow passing at last over that affable face, "I am pretty calm, but nobody has pushed me yet to go over that limit. Perhaps," he adds, and I take it as a dismissal, "that is still to come."

'Der fliegende Holländer' opens at the Royal Opera House, Covent Garden (www.roh.org.uk), on 23 February