Golf was to have been the hors d’oeuvre. In common with several other leading opera singers, Bryn Terfel enjoys swinging a club for relaxation, and I had been promised an invitation to Sunningdale, the exclusive golf club in Berkshire where he is a member. We were to eat at the sausage hut on the ninth hole, where players stop off before finishing the course. But the Royal Opera House has landed Terfel with an unexpected afternoon rehearsal - even stars with his pulling power get no special dispensation - and he must be there at 2.30pm prompt, ready to impersonate the sly rogue who cheats an entire family out of their inheritance in Gianni Schicchi.

The title role in Puccini’s comic one-act opera is a departure for Terfel. Most audiences know him as an interpreter of classical song. He shot to fame at the 1989 BBC Cardiff Singer of the World competition, and has won critical praise in the operas of Mozart and Wagner, which suit his richly coloured bass-baritone. But international acclaim as Verdi’s Falstaff and Puccini’s Scarpia, in Tosca, have made Gianni Schicchi an obvious next step.

The call of high art seems far from Terfel’s mind as we settle into the downstairs lounge at Roka, an Asian-style restaurant 15 minutes’ walk from Covent Garden. Terfel, his bulky frame softened by a camel-coloured rugby shirt, can just about wedge his knees beneath our table. But even if it were lower, you could hardly imagine him complaining. Terfel is a Shrek-like giant, all gentle manners. As befits a 41-year-old with the world at his feet, he seems at ease with himself - and with chopsticks.

As well he might: he has just returned from a tour of Asia. ”You become engulfed in their food,” he says, also admitting to a fascination with Saturday-morning cookery shows on British television. ”In a profession that involves so much travelling, food and drink always come to the forefront. In some restaurants [in Asia] you are totally in their hands.” But not in Roka, judging by the way Terfel merely glances at the menu. He has been here before, having been introduced by Pink Floyd guitarist Roger Waters while recording Waters’s rock opera Ca Ira in a nearby studio, so he knows pretty much what he wants. We agree to share a variety of smaller dishes, Terfel’s only caveat being that if I have ”important” meetings later in the day, garlic should be off-limits. I don’t, so aubergine joins the selection.

Terfel has no qualms about garlic, despite the prospect of rehearsing at close quarters with the cast of Gianni Schicchi. And he seems equally unfussed by accusations that his ”crossover” CDs - a mix of hymns and mood-songs in easy-listening arrangements - show a lack of taste. In the eyes of many classical music critics, including me, Terfel’s populism is his Achilles’ heel. It’s as if half of him is a singer of refinement and range, and the other half a country boy with both eyes on the main chance. He does his best to combine the two at his festival at Faenol in north Wales, where he grew up on a sheep farm and now has the status of local hero.

Here, then, is my opportunity to ask: would he rather head downmarket and achieve the huge commercial success of Andrea Bocelli, the tenor shunned by most classical promoters, or does he see himself as a singer who serves art? The two are mutually exclusive, I suggest. Blithely ignoring my debating gambit, Terfel springs to Bocelli’s defence. ”I had a deal with him,” he says, the majestic warmth of his voice somehow working against the cold thrust of my argument. ”I let him sing on my album, and he agreed to sing at my festival. It was the first time we sold all 12,000 tickets for an opera night. He’s an amazing musician.”

I am about to tell Terfel I do not share his enthusiasm for Bocelli, but our attention is diverted by the arrival of plates of chicken, lamb and salmon, taking up every available space on our table. As we make an easy division of spoils, Terfel starts singing the praises of another tenor, Rolando Villazon, a favourite at Covent Garden and most other leading opera houses. ”If you think I’m an entertainer, he’s three-fold. When Rolando came to Faenol he started juggling in the middle of our Elisir duets. He didn’t tell anyone beforehand, but suddenly he brings three oranges out of his pocket. I’ve never heard anyone sing A-naturals like that.”

So much for Terfel’s high-profile friends from afar. It seems the right moment to ask about his high-earning Welsh compatriots Katherine Jenkins and Charlotte Church, both of whom have been dubbed ”opera singers” without ever having set foot on an opera stage. Surely Terfel would not want to share a platform with such manufactured stars? On the contrary, he says. ”They’ve filled a niche. I heard Katherine on the radio recently. They played Maria Callas and Katherine, one after the other, singing the same aria, and asked listeners which they’d like to hear again. Katherine won the vote.”

Are we to deduce, then, that Jenkins is the greater artist? ”People are buying her albums, and that might open the door to an opera house,” says Terfel, savouring the taste of a New Zealand wine whose name he remembered from a previous visit. ”I had 170 supporters from Wales come over to New York to hear my Figaro at the Metropolitan Opera. A high percentage of them would never otherwise have gone to an opera house.” And the likelihood is they will never return, I interject, unless Terfel gives them another reason to go. ”It was a good enough reason for them to visit a city they’d never been to before,” he counters. ”I always make sure they do their [pre-performance] homework.”

You can’t help admiring Terfel’s uncomplicated view of life, apparently untouched by the dramas of the profession in which he moves. I tell him that the evidence of the Three Tenors - the 1990s stadium concerts given by Jose Carreras, Placido Domingo and Luciano Pavarotti - was that, while their populist approach generated phenomenal CD sales, it did not translate into higher attendances in opera houses. At the English National Opera, for example, audience figures have declined over the past 15 years. I wonder aloud whether Terfel has blindly swallowed his record-company publicity.

He pauses - a cue for downing chopsticks and eating lamb cutlets hand-to-mouth. ”I know the record industry and what it’s about,” he says. ”If there’s a bandwagon, certain people won’t hesitate to jump on it. I was guilty in the Mozart year [the 250th anniversary of Mozart’s birth, last year]. But if Katherine Jenkins sells half a million CDs, her record company will clothe her and give her a life. The way careers develop today, you have to have these attributes [of catering for all tastes]. I hate being pigeonholed - I’ve never said I’d concentrate on one aspect of the profession. On my first day at the Guildhall [the London music college where Terfel trained], I was given a schedule that included opera, tap dancing, fencing, jazz and oratorio. It was like a huge silver tree, one of whose branches you were supposed to fit like a glove. I felt comfortable with most of them right from the start.”

The time has come to share out the leftover salmon and aubergine, which Terfel does as deftly as he wields his chopsticks. ”I just take on what I enjoy,” he continues. ”How I’m labelled doesn’t matter. Any record company would be extremely happy with sales of 100,000 for a classical album, but Bryn [a mixture of classical and pop] has sold 800,000. If my company wants to do something a little out-of-the-ordinary, I’ll say yes, but only if I’m 100 per cent behind it and it comes with what I need” - a reference, he quickly explains, to the orchestrations he commissioned from another Welshman, Chris Hazell. ”I think I know where to draw the line. If someone asked me to do an Elvis crossover, I know what the answer would be.”

That’s not the only line Terfel has drawn in his career. He has long maintained that he will retire from opera at 45 - an age when most of his great predecessors were reaching their peak. Married to his childhood sweetheart, he has three young sons and Terfel has already cut his transatlantic visits to one a year. ”I’m sad that I don’t have what some of my colleagues have - the ones who live in a city where there’s an opera house, and you can go home to your own bed at night and have breakfast with the kids in the morning.”

There’s no time for pudding but it takes an unconscionably long time to get the bill. With Terfel’s rehearsal due to start in fewer than 15 minutes, I seem to be more in a flap than he. Still chatty as we head through London’s West End towards the Royal Opera House, Terfel describes his taste as ”traditionalist. What I like is something that pleases the audience. Last month I came out of Falstaff thinking, ’That’s the best I’ve ever sung,’ but the thing that interests me as a performer is what percentage of the audience thought exactly as I did. In Vienna, there are hundreds waiting at the stage door to tell you. Some have seen all the shows going back 40 years. They pass on tips of the trade - like in act two of Tosca, the way Tito Gobbi ran the feather-quill of his pen right up Callas’s body as she stood by his table. Whoaaa! How did I miss that when I saw it on film?”

We arrive at the stage door a full 15 minutes late. Terfel’s parting words are that he will ”smile and apologise profusely” to his colleagues. I already know their response: they won’t be able to stop themselves smiling back.

Roka, London W1

2 x eggplant

1 x salmon teriyaki

1 x chicken skewers

1 x lamb cutlets

2 x rice

1 x tomato juice

1 x mineral water

1 x Seresin Sauvignon Blanc

Total: ₤70.48