McCall Smith was born in Zimbabwe

The £20,000 prize was open to all British writers aged 50 and over whose work made the judges laugh.

The 55-year-old scooped the award for his book, The Full Cupboard of Life, the fifth in his series of novels about a female detective from Botswana.

The judges, including actress Penelope Keith and broadcaster James Naughtie, said his work was "a miracle of gentle wit and perception".

McCall Smith, a professor of medical law at Edinburgh University, was up against big name authors including Sir John Mortimer, Keith Waterhouse, Mavis Cheek and 90-year-old journalist WF Deedes.

African roots

The award was announced at the Folkestone Literary Festival in Kent on Monday night.

McCall Smith had written over 50 books by the time he published his bestseller, The No 1 Ladies' Detective Agency, the first of five novels about Precious Ramotswe, the only female private investigator in Botswana.

The lecturer was born in Zimbabwe and went to school in Bulawayo, near the Botswana border, before moving to Scotland to study.

He returned to Africa to help set up a law school at the University of Botswana before settling in Edinburgh.

McCall Smith has recently finished the first book in a new series featuring another female detective, Isabel Dalhousie.

The first title, Crushed Strawberry, will be published next year.