"My grandmother used to tell tales of their lives here and I thought some of them could be shifted and shaped into authentic characters. I didn't tell their actual stories though. I made up my own. It is probably a good thing that none of them are alive to read the books though," he laughs.

The first one of the series sold 100,000 copies and in bookstores around the world they still hold their positions on the shelves of this narrow genre of Chinese historical fiction written by Westerners.

"China until recently has been rather sort of a specialist interest. There were quite a few writers in the 1920s. You have Robert Van Gulik with his Judge Dee historical mysteries in the 1930s. Various journalists have also written novels," he says.

Williams, who was born in Hong Kong but went to Radley College, the English public school, and then Oxford University, where he read English (where the lecturers there included Iris Murdoch and WH Auden), began his career as a journalist at the South China Morning Post in the late 1970s.

He quickly switched to business, however, finally ending up as group chief representative of Jardine Matheson, a company inextricably linked to China's history via its associations with the Opium Wars in the 19th century. He stood down in 2015 but remains an adviser.

"It has sort of moved on from firing people for not selling opium on a Sunday," he laughs. "It is a very modern company now, a services conglomerate now into real estate, insurance, hotels, retail and supermarkets. Many of Jardine's companies you know by their other names, like the Mandarin Oriental Hotel, for instance."