SHE was born near Bristol and spends much of her time in London, nevertheless JK Rowling has long been regarded as an honorary Scot. Now, it has emerged that the Harry Potter author has a legitimate claim to Scottish ancestry.

Rowling is believed to be the great-granddaughter of Dugald Campbell, a pioneering doctor from Arran who helped establish the national health service in Hawaii.

The surprising discovery follows months of research by Anthony Adolph, a genealogist, who claims to have traced Rowling’s roots back as far as the early 19th century.

Rowling, who is joint 96th in The Sunday Times Rich List with a personal fortune of £500m, is reported to have contacted historians in Hawaii to find out more about her ancestor and to have made an emotional pilgrimage to the family plot in a graveyard at Lamlash on Arran.

According to the research, Campbell, a graduate of Glasgow University, travelled extensively, moving to Hawaii where he took up the post of government physician and raised money to establish a hospital where the islanders could receive free medical treatment.

He moved to London in 1915 and is said to have had an affair with Mary Smith, a young book-keeper, and fathered Rowling’s grandmother.

The girl, Louisa Caroline Watts Smith, who was renamed Freda by her adoptive parents, was born at a private nursing home in London on May 16, 1916. Her mother disappeared soon after giving birth.

Freda was raised by the Watts family, who owned the nursing home, and was told her father was a Dr Campbell. She married Stanley Volant, an engineer, and gave birth to two daughters — Anne, Rowling’s mother, and Marian.

Campbell died in 1940, aged 82. Anne died in 1990 at the age of 45, following a long struggle against multiple sclerosis.

“We think it is a strong possibility Dugald was my grandfather — Jo’s great-grandfather,” said Marian, who lives in Watford. “Jo was keen to trace him and has done a bit of research as well.

“She has been to Dugald Campbell’s family grave on Arran and now we hope to go up there together and look at the local records to find out more about him.”

Rowling is married to Neil Murray a Scottish doctor and has homes in Edinburgh, Perthshire and London. Last night her publicist decline to comment.

The research into Rowling’s ancestry, coincides with one of the biggest studies of inherited wealth in Britain, to be published this week. It reveals that one in five of the population can trace their ancestry back to a family much grander and richer than themselves.

While half of those who used a new computer system to research their family tree back as far as 500 years found that they were upwardly mobile, at least 20% discovered that their ancestors had made (and then lost) a great fortune.

Genealogy sites have become some of the most popular on the internet and an analysis of the family trees drawn up by more than 1,000 people who used Genes Reunited, an offshoot of the Friends Reunited website, to trace their ancestors has provided a unique study of social mobility dating back to Tudor times and beyond.

“It is a representative sample of people living in this country and shows the change in the workings of British society down the ages and also the workings of families, which don’t really change,” said Adolph, the genealogist who led the project.

“People make bad decisions, they squabble, they take disastrous legal action or they are just plain lazy.”

Tracing family trees used to be the preserve of the upper middle classes, but the advent of computer databases has allowed everyone to have a go.

Tracey O’Connor, 44, who was born in a Leicester council house and has worked at a local Sainsbury’s supermarket for most of her adult life, is one of those who discovered they are members of the “new poor”.

“I’ve always thought I came from a solidly working-class family, but I was amazed to discover we’re descended from the owners of West Indies sugar plantations and East Anglian estates, as well as surgeons, army officers and magistrates,” she said. “They lost all their money and were in the workhouse by the 1880s, but I can’t find out why.”

Adolph’s great-great-great-grandfather was James Paterson, from Selkirk, who founded one of the most successful and well-known luggage haulage firms in the country “He was one of the great Scottish entrepreneurs who made a huge amount of money which I put down to hard work and the determination to succeed.” he said.

However, the wealth dried up when the company was nationalised during the first world war and the stocks declined during the depression of the 1920s and 1930s.

Times Recommends

• Family cuts its waste to one binful a year
• Cameron can learn from Thatcher in 1979
• VAT is back ... and it's confusing