Alexander McCall Smith interview: The No1 bestseller agency

Next to it, there's a large, plain white bookcase. Elsewhere in the house, the shelves are testament to a formidably well-stocked mind, but these ones are different. This is where McCall Smith keeps copies of his latest editions, often in some of the 42 languages in which they have been translated. As we talk, his secretary brings in a sheaf of contracts to sign from his agent. One is for a Bulgarian translation of his No 1 Ladies Detective Agency novel. In time, no doubt, that will find its way onto the shelves facing him too.

The books here are different in another way. Unlike the dull-covered tomes on poetry, ethics, philosophy and law, they blaze with colour. It's as though the world's publishers have independently decided that books that are, like his, brim-full of what Boswell called "all the sweets of being" should be colour-coded with jaunty yellows, promising pinks, and optimistic light blues.

I'm talking to him about Tea Time for the Traditionally Built, the latest addition to those bright, ordered, shelves and the tenth in his world-conquering series of books set in Botswana. And before you raise a hyperbole-sensitive eyebrow, consider the following two facts. Last week the last book in the series was Britain's best-selling novel in paperback. And next month the TV series based on McCall Smith's Botswana novels will be showing in the coveted Sunday evening prime-time slot not just on BBC1 but in the US too, on HBO.

So if you sit, as he does, in a study facing that battery of bright, best-selling books, and in front of a capacious computer on which he will play the preview discs of the TV series when they arrive any day now, that's the view. That, for any writer, is what success looks like.

Has it changed the way he writes? "It's a liberation," he replies. "Before, I was very conscious of the fact that what I was writing was not necessarily what people expected from a Scottish writer and not necessarily what was wanted. Now I feel that I can write exactly what I want and not worry about whether or not that will meet with approbation from editors."

Compare the first two titles and the later ones and you can see what he means. The first Botswana books gracefully opened up a corner of Africa unknown to readers in the West and populated it with characters such as Mma Ramotswe – about whom, they discovered, they cared very deeply.

Oddly (to a reader, though most writers will understand), McCall Smith says he has never had a clear picture of Mma Ramotswe in his mind. He can remember well the moment, nearly 30 years ago, when he saw a large woman – "traditionally built" in his own exquisite euphemism – scampering round her yard in Botswana, chasing a chicken as a gift for a friend.

That memory resurfaced years later, when he first started writing The No 1 Ladies Detective Agency, so that kind African stranger has some claim to being the "real" Mma Ramotswe. So too does Jill Scott, the American actress and jazz singer who plays her in the TV series, shot entirely on location in Botswana. Yet when he thinks of Mma Ramotswe, he admits, he doesn't think of either woman's face – or indeed, anyone else's.

If that's missing, everything else about her world is affectionately detailed. He loves Botswana, and it shows on every page. But it's the country's older values that both he and his readers respond to most deeply. This is a place where there's time to talk, where nothing much happens, where there are no strangers, and the living fondly remember the dead. In an alienated, rushed, busy, self-obsessed world, who couldn't warm to that?

Except with McCall Smith, it's felt, not formula. Readers can tell the difference. They're not really drawn in by plot – it's as necessary, he admits, as a tune is for resolution in music – so much as by character. And this is where his series scores. Put Mma Ramotswe in her office talking to Mma Makutsi about men's foibles over a cup of red bush tea, and most of his readers mightn't ask for anything more. Cake, perhaps.

So when McCall Smith goes to book festivals to spread the word about Tea Time for the Traditionally Built, he doesn't need to whet his audience's interest by explaining how his heroine tackles her latest case, which involves allegations of match-fixing against the Kalahari Swoopers football team. All he needs to do is to give the briefest of readings – sometimes no more than a page. The audience, wanting to ask him about favourite characters, does the rest.

"One thing you learn," he says, "is that the larger your readership becomes, the more you lose ownership of the characters. I was in Sydney recently, for example, and at an event two women told me that they disapproved of Isobel's relationship with the (much younger] Jamie in the Isabel Dalhousie series. 'That's not going to last!' they said. I replied that I thought it was all going quite well. 'It isn't!' they said. Such things make you realise that the characters you've created are now the property of millions of people who all have a notional stake in them and become intensely involved in what happens to them."

He knows just how intensely from the letters he's received from people thanking him for the enjoyment his books gave to loved ones on their last days on earth. "I take that very seriously. I don't make light of people's involvement – anything but.

"That's why I regard it as incredibly condescending to think of these books as escapism. These books are about really serious matters. Even Scotland Street is." My own hyperbole-sensitive eyebrows start to raise, because I know full well how this newspaper's "daily novel" (see panel) has also given full rein to McCall Smith's quirky, witty, gently comedic view of the world. Then I remember the way in which some scenes – Ramsay Dumbartan's death, for example – fused comedy with altogether deeper emotions, becoming even more moving in the process. So I nod instead.

If you want to understand McCall Smith's literary aims, a good place to start is an introduction he wrote last year to a republished edition of Barbara Pym's novel Excellent Women. In it, he praised her as a chronicler of the kind of quiet lives often neglected by mainstream literary culture, expressed delight in the way in which she turned the tiny things of daily life into comedy, and steered her own course away from the obvious topics of the day.

There's an obvious parallel with his own work there, but he puts it differently. "I'm interested in character and dialogue and exchange of ideas. If I were to look for a glib description of what the books are about, I'd say they're a form of what in painting is called intimisme – those paintings by painters like Vuillard and Bonnard in the 1890s of intimate little domestic scenes. I don't consciously set out to do that, and I don't produce this as an apologia, it's just that this is what the stories are."

Art, readers of McCall Smith's two Edinburgh-based series must have noticed, suffuses his plots, so it's no surprise that he reaches for another painterly analogy. "It's like those interiors in the golden age of Dutch painting, when you look through a doorway into another room. The capturing of that quiet space strikes a chord with people. The reason why people read these books is that they want to spend time with Mma Ramotswe in that quiet space. And in order to do that, one has to take certain liberties, to limit the character's world, or take it out of somewhere completely real."

That's what happens in Tea Time for the Traditionally Built, as no doubt it will for the four other books he is contracted to write for the series. Unlike his near-neighbour JK Rowling, he has no end scene in mind for his series; unlike his next-door-but-one neighbour Ian Rankin, he has never agonised over when and how to bring the series to an end.

For the moment, though, Mma Ramotswe will carry on sorting the smaller problems in her clients' lives under a cloudless blue Botswana sky. That is what she does, with just a few new embellishments each time, but always the same humanity, humour and charm. And her creator has only to look up from his keyboard at that wall of brightly coloured books to realise that is what almost all of the world wants her to carry on doing.

Tea Time for the Traditionally Built by Alexander McCall Smith is published by Little, Brown, priced 14.99. A six-part, one-hour drama series based on The No 1 Ladies Detective Agency books starts on Sunday 15 March on BBC1.

44 Scotland Street returns in the autumn …

ALEXANDER McCall Smith is to resume his 44 Scotland Street daily novel in The Scotsman this autumn and has already written the first three episodes, he has revealed.

His notebooks contain a number of new plotlines for the characters in the five-book series, which has now been translated into several languages. The latest in the series, The Unbearable Lightness of Scones, was a New York Times Top Ten bestseller.

"Wherever I go in the world," he says, "people all know about Scotland Street and are always asking me about what's going to happen to the characters next. Bertie in particular seems to have developed a worldwide following."

"We're delighted to welcome back 44 Scotland Street," says John McLellan, editor of The Scotsman.

"It was a first for British journalism when Sandy's daily novel started in this newspaper in 2004, and we're glad that our readers will still be able to get the first glimpse of the new book in a series that has captivated readers throughout the world."