ALEXANDER McCall Smith has expressed his sadness at how Scotland has become divided by the independence referendum.

While not revealing which way he will vote in September, the best-­selling author of the Mma Ramotswe novels and ­Scotland Street books said that he felt sadness that the "very difficult issue" had split the country.

"Scotland is now a divided country," he said.

He told an audience at the Edinburgh International Book Festival that he would not be introducing any ­referendum themes into his books.

The writer said: "I feel very strongly that I shouldn't, in those books, espouse any political position.

"There are references to issues which are political in the general sense but I think it would be a bit of an abuse of my situation to use it to expound on my private views.

"I know it's a tricky issue, a very difficult issue for people in Scotland and I think I would prefer not to bring that into the books.

"I think it's a sad situation that Scotland has become so divided."

"We are now a divided country ... one of my ­characters declares himself a 'Scottish patriot but I feel it's very important that it does not affect my affection for our neighbours' and I feel that is very true."

McCall Smith said he was working on the libretto for a new opera about the Soviet spy Anthony Blunt which should be completed next year.

The two main female ­characters will be the late Queen Mother and Margaret Thatcher, he said.

"It's really exciting because there is so much to that story," he said.