For a moment my interview with Thomas Quasthoff threatens to turn a bit OK! magazine. The German bass-baritone is gushing about his wonderful new wife, the joy of being a father, their beautiful new home in Berlin. But there’s more to Quasthoff: a sharp wit, spiky opinions and a startlingly matter-of-fact attitude to his personal story. Quasthoff was a Thalidomide baby. He is 4ft 3in, and when we meet he wears miniature jeans, polo shirt and a short-sleeved tweed jacket tailored to his tiny arms.

Quasthoff has just heard that he will receive the Royal Philharmonic Society Gold Medal — its highest honour, bestowed on the likes of Daniel Barenboim and Placído Domingo — confirmation of his place among the classical world’s elite. He already has three Grammy awards and his current, sold-out residency at the Barbican in London is wowing audiences and critics alike. It is one of fewer recitals now, as his family becomes a priority.

“I married at 47 and I realise that for me, family life is more important than any musical event,” Quasthoff says. His wife of three years is Claudia, a Leipzig journalist; they met when she was sent to research him for a talk show. “Now it is much nicer to say no to engagements, knowing that what I have now, if I’m not going to a concert, is satisfying me so much more than waiting in airports, staying in bad hotels. And Lotte [his ten-year-old stepdaughter] deserves that I’m not a guest at home.”

The Barbican concerts, however, promise musical discoveries for Quasthoff. It will be the first time, for instance, that he has sung with Valery Gergiev (as the Devil in Berlioz’s La Damnation de Faust, in September). “We met permanently at festivals and every time he said: ‘We have to work together.’ I said: ‘You know, work together means we have to have rehearsals,’ ” Quasthoff jokes.

But first he sings Bach’s St Matthew Passion. Quasthoff loves the work’s meditative qualities, compared with the more dramatic St John Passion. “Erbarme dich is one of the greatest alto arias I know,” he says. Is he religious? “Me?” he splutters. “No. I believe much more in love and tolerance. But I understand the feelings, I understand the music — mostly. The St Matthew Passion is like going inside a big church; every time you enter it seems larger. This music is astonishing; it’s full of emotion and it goes deeply into the hearts of the people.”

Quasthoff’s recitals do the same, mainlining emotion to his audience. Hearing him sing the Bach Cantatas and Handel’s Joshua at the Barbican was to see a man brimful of music. There is simply no room for starry pretension or posturing — only honesty. His voice floats lightly to top notes, but is deliciously rich on the bass. And as for vocal characterisation, listen to him sing Schubert’s Müller lieder, where his baritone shifts from joy to despair.

Appearance is irrelevant when he sings, and I wonder if performances and their glowing reviews aren’t a respite from what could crassly be termed the Quasthoff baggage: the Thalidomide baby made good. In his autobiography, The Voice, and in countless interviews, Quasthoff has told his story in typically blunt style. He spent most of his first two years in an isolation ward, his family unable to speak to him. For four years his legs were clamped in a cast to force his feet to grow the right way round. Against all prognoses, his mother (who died in January) taught him to walk by tempting him with chocolate.

And there were rejections: from normal school, marooning six-year-old Tommy in a boarding school for the disabled. Yet he was always musical and his parents paid for singing lessons (his father’s own singing ambitions were thwarted by the war). When he applied to Hanover conservatoire, however, Quasthoff was refused because he couldn’t play an instrument. He funded his own lessons and when he won a prestigious singing competition in 1988, the classical world took notice.

Every person is the sum of their experiences and upbringing, and Quasthoff has an astonishing self-belief. “The thing that came from my parents was always: if you want to become a singer, you have to work a little bit harder, be a little bit better because of your disability. I’m absolutely sure that my mother, for example, couldn’t imagine that I would be able to be on stage. I remember one night when I heard her crying and saying [to his father]: ‘Are we doing the right thing to encourage him to be a singer?’ Seeing me as Amfortas in Parsifal, with the Vienna State Opera — it was a positive shock for my mother.”

Encouraged by Sir Simon Rattle, Quasthoff sang Don Fernando in Beethoven’s Fidelio, but he will not do more staged opera. It’s not for want of offers:

“Vienna State wanted me again; to sing Wotan, for example. I said, definitely not my role. It’s too big.” Does he mean physically? “No. Vocally it’s not my role. I’m not this kind of black bass.” He won’t be drawn on a role’s physical suitability, though he once refused Wagner’s dwarf king, Alberich, explaining: “Maybe it’s more important for me than for others to choose what I want to sing.” For now, he will only add that he’s not prepared to spend the months away from home that opera requires.

Increasingly, the classical world — and especially opera, magnified on the world’s cinema screens — puts a premium on good looks. What chance, then, for a disabled artist today? “It depends how good he is. Very simple,” Quasthoff shrugs. He is not about to become a mouthpiece for disabled artistic rights. “As long as you’re good, nobody can raise their nose and say: ‘Oh, it is because of his disability.’ And I know there are people around arguing like this.”

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