“When I was 10 I read The Secret of the Unicorn,” he confesses. “But it ended before the treasure was found, and I spent all year in a state of tension. We glimpse the Round Pond between the trees, the bear fountain, and we are nearly at the doors of Selfridges and the “lapis-robed statue” that looks down as our hero, Michael, sees a fugitive face, a great lost love from 10 years earlier in another 94 bus.But we pass the angel of Selfridges in silence, and at length Seth gets off the bus at Bond Street.”What is your favourite Tintin book?” he has been badgering me. And so this is how it is when the interview is over, and we end up on the 94 bus together on the top deck, and a magical mystery tour of An Equal Music begins. He finds it difficult to encompass the extravagance of – say – taking a taxi anywhere. “After Suitable Boy, it’s difficult to say the word,” he says, a little mysteriously.He’s used to the fame now, but even with the money (“I made a pot of money”), years of penny-pinching has left its mark.

Hang on, isn’t that a bit cold? “Yes, I’m part of the club allowed to swim there.” They have to sign health waivers with the local council before dipping a toe in those goose-turded waters. “I tend to go on a Saturday and we do handicap races and swim around the buoy,” he tells me He pronounces buoy “boo-wee”, like an American Why does he do that? He flushes a little. Of course, there is that scene where the two lovers, many years on, meet briefly and by accident. It’s a bit like the one in his new novel.Another exertion he’s fond of, and which pops up in the novel, is swimming in the Serpentine In the winter. Having taped the film off late-night TV, Seth sat down “with my hand on the pause button and a handkerchief” and allowed himself to weep his way through a weepy classic. It turns out that he recently learnt French, in Kensington, at the French Institute, and used Tintin and Les Parapluies to train himself.

“Maman est morte en automne,” he trills in a fine baritone, throwing out his hands in ecstasy. He immediately and spontaneously starts singing snatches of it with a kind of helpless pleasure. With its amazing splashes of colour and its slightly kitschy operetta style, the film would, you might have thought, be a million miles away from the sensibility that doggedly fashioned A Suitable Boy.But Seth is electrified by the merest mention of the film It’s absolutely his movie du jour. He once trained to play the Indian flute, but “I’m not even a medium-level amateur,” he tells me. While trying to “distract” himself from writing, he learnt to sing Schubert lieder, but does not think to let me hear his voice until, by complete chance, I mention the vivacious 1963 musical Les Parapluies de Cherbourg, Jacques Demy’s light-as-a-feather confection (with Catherine Deneuve in her first major role, as a singing shop girl). “Verdi, I think, but why Verdi? Oh, it’s Vicks, because I have a blocked nose”.Verdi is no doubt too florid for his musical tastes, which tend towards the simple expression of deep emotion. It’s not that Madonna Hindi thing, is it? Those Sanskrit signs Madge has taken to drawing on her hands? Are we back on Salman Rushdie again? Seth peers owlishly at his smudged palm “No, no,” he announces at last.