Alexander McCall Smith’s books are easy on the eye. Words flow. Characters leap from the page. The impression is that his worlds come easily to their creator. The man himself confirms this, while being aware that authors are not supposed to be so blessed.

He says: “I was once doing an event in America at a college. I was talking to a group of students. This young man at the back looked at me and said ‘Do you suffer? ’ I said ‘No, not really.’”

McCall Smith chuckles at the memory. Suffer? Why on earth would he do that? His books are fun for him as well as his readers.

“People sometimes think writers sweat it out and go through all sorts of agonies. I don’t really have to agonise. I don’t think I have to strive too much. I am conscious of my good fortune in being able to write quite quickly.

“It flows quite nicely. I write something like five books a year. My problem is almost having too many things I can write about.”

The 68-year-old sounds as genial as most of his characters. He creates stories laced with humour, charm and moral messages, subtly delivered.

He specialises in long-running series. His 17th No. 1 Ladies’ Detective Agency title has just been published. These are set in Botswana and feature female private investigator Precious Ramotswe.

The locale is well known to McCall Smith. He taught law at the University of Botswana, having been brought up in neighbouring Rhodesia.

He then taught medical law at the University of Edinburgh, where he had studied, and became a full-time writer when his novels took off.

Two other series – 44 Scotland Street and the Sunday Philosophy Club – are set in Edinburgh, which remains home to him and his wife Elizabeth, a retired GP. Neighbours, and friends, include JK Rowling and Ian Rankin.

McCall Smith will be south of the border, if only just, next Thursday as the opening act of this year’s Borderlines Book Festival.

It’s a coup for Carlisle to attract one of the world’s biggest-selling authors. McCall Smith’s books have been translated into 46 languages, and have sold more than 40 million copies.

Does he ever think about these extraordinary numbers?

“Not really,” he says, on the line from his house, having just shooed a cat from the room.

“You can’t really think too much about these things. You can’t really think too much about what you’re doing.

“I think sometimes that it’s like walking on a tightrope – not that I can do that. But when you’re on a tightrope you don’t look down.

“I don’t look down. I am aware that I’m addressing a large number of people. I am aware of the responsibilities that go with that.”

He feels that these include trying to add to the world’s supply of happiness. The thought that he might succeed in this mission is a source of delight.

“I get great pleasure from that. Every day I get letters and messages from all over the world. The things they say are often quite moving, particularly about The No. 1 Ladies’ Detective Agency.

“They say Precious Ramotswe has helped them in some way at a difficult time in their lives.

“I take that very seriously. That’s probably the reason why I do it, that these books might contribute to people’s happiness.

“I wouldn’t want my writing to cause anybody distress. There’s room for all sorts of things in literature. Books which are bleak and harrowing – that’s part of the spectrum.

“I read pretty broadly. I can read things which are bleak, but I don’t have to write them.”

The relationship with readers is clearly important to him. He enjoys meeting them at events, and is even willing to accommodate their ideas.

“Sometimes suggestions will be made which I can use. I have on occasion said ‘Yes, that’s fine. We can have it work that way.’ Sometimes they want me to eliminate a character they don’t like.’”

He laughs again. A popular candidate for this fate is Irene Pollock; the smothering mother of eight-year-old Bertie Pollock in the Scotland Street books.

“People sometimes say ‘Bertie’s suffered enough.’ I know what they mean. Sometimes they want me to dispose of Irene. But we can’t have Bertie deprived of his mother.”

He adds: “People can invest very heavily in characters and want to see what’s going to happen to them, particularly in serial novels.”

At Edinburgh International Book Festival last month, one woman asked the author why he doesn’t write about political issues rather than “trivia”.

A murmur of disapproval ran through the adoring audience.

Reminded of this, McCall Smith’s response is similar to that which he gave at the event.

“You can get people to think about profound issues, to think about being human, without landing them with things which are bleak and too heavy.”

He does this in books for children as well as for adults. And in addition to his series there are several standalone novels.

The latest, My Italian Bulldozer , concerns a writer arriving in Tuscany to find no trace of his hire car. Alternative transport is provided. This is based, somewhat loosely, on McCall Smith’s own experience.

“I very much enjoyed writing that. It was a joie d’esprit . A bit of nonsense, but a great deal of fun.”

Producing five books a year means writing up to 5,000 words a day, a quantity far beyond the majority of authors.

He says: “I tend to write in the small hours. I get up at three or four in the morning. I get quite a lot done then go back to bed at 6.30 for a few hours.”

There is also a touring schedule which would shame most rock bands. Does his wife think he works too hard?

“She will generally say that I do too much. I think she might take the view that I should do a bit less.”

He admits: “It’s difficult with the touring. I try and keep it sensible. But I really enjoy it.”

The world is littered with would-be novelists. What advice is offered by a man who has completed the task so often?

“Persist,” he says. “And I think a lot spend too much time on their first manuscript. They rework and rework. They need to go on to their second and third books, because those will be better.

“Also, try to take the first person out of it. A lot of people put a lot of themselves into it.”

McCall Smith’s No. 1 Ladies’ Detective Agency books are, not surprisingly, bathed in sunshine. But so are his Edinburgh novels. Reflecting the writer’s outlook on life, all are set in summer.

“I suppose the reason for that must be, the Scottish summer is brief and beautiful. That suits the feel of the books.”

* An Evening with Alexander McCall Smith takes place at the Crown and Mitre Hotel, English Street, Carlisle, on Thursday September 29 at 7.30pm. Tickets £9 from Bookends, Castle Street, Carlisle, or call 07412 366125.