But all has changed since Swedish police swooped on London in search of the pounds 50m that has gone missing from the Stockholm investment company Guinness took over last summer.
Contrary to the press release accompanying the release of Requiem for a Family Business, published on Friday, the 67-year-old scion of the Irish brewery dynasty is not available for interviews. Nor did he return telephone calls all week.
Swedish authorities this week said they believe the missing funds were transferred from Trustor's Swedish bank accounts to an account at Barclays Bank in London shortly after Guinness took control.
The mystery of the moment - apart from the whereabouts of the money - is why Jonathan Guinness would suddenly go on a Scandinavian spending spree. In June, he paid about pounds 19m for control of Trustor, which invests in companies that make engineering and car parts, such as AP Parts, UP Parts, and TPC.
Then, in early June, he offered pounds 34m for a controlling stake in Finnish sporting goods group Amer, makers of Wilson tennis rackets and Atomic skis. That deal fell through.
Although Jonathan Guinness served as a director on the Guinness board for 27 years, it's not his business acumen he's primarily known for. Rather, it's his vociferously right-wing views and his unorthodox personal life that have gained him a reputation as a wild card.
A complex, contradictory man, his somewhat meandering career path included an early three-year stint at Reuters, training at Erlangers, a directorship at merchant bank Leopold Joseph and an unsuccessful bid for a seat in Parliament.
Aside from the new book on Guinness, he has written two others - an account of his mother's legendary family, the Mitfords, and the life story of his long-standing mistress, a Sixties flower child named Shoe.
In his latest book, Jonathan Guinness portrays not only the turmoil and legal wrangling surrounding the company's takeover of Distillers, but also the way the Guinness dynasty was gradually marginalised from the brewery and distillery business it had controlled for more than two centuries.
When his father, Bryan Guinness, died in 1992, Jonathan Guinness became the third Lord Moyne. Playing the part of family patriarch was never his intention, however. He was always too much of an iconoclast.
At times he has assumed the role of an arch right-winger, upholding time- honoured virtues of reward and punishment, social hierarchy and stability. He served as chairman of the Monday Club, a conservative Tory pressure group, for two years.
In 1973, when standing in the 1973 Lincoln by-election, he called for razor blades to be placed in the cells of convicted murderers. It earned him the nickname "Old Razor Blades."
Then there was his revelation in 1989 that he had been living a double life. While married to his wife of 25 years, Suzanne, he was maintaining a second family with Shoe Taylor, a globe-trotting free spirit he met in a Spanish resort in the 1960s, and with whom he had three children. The book he wrote about her was called Shoe: The Odyssey of a Sixties Survivor.
He said he wrote it to forestall a nasty tabloid smear. The Sunday Express "had dug up the first child," he said, "but there were two more for someone else to discover. I felt that a controlled explosion by myself was best. I was caught on a ledge, and I had to leap."
Yet the book only fuelled his reputation for unorthodox behaviour. In that regard, he perfectly fits the family mould.
His parents, Diana Mitford and Bryan Guinness, were the toast of literary London in the early 1930s, but the marriage ended when Diana fell in love with and eventually married Sir Oswald Mosley, the British fascist.
Jonathan was a 14-year-old schoolboy at Eton when his grandfather, the first Lord Moyne, was gunned down by Zionist zealots in Cairo in 1944.
The family has experienced more than its share of bizarre tragedies, including drug overdoses, suicides, car crashes, a drowning in a bathtub and a kidnapping.
It was Jonathan Guinness's cousin, the third Earl of Iveagh, who as chairman of Guinness recruited Ernest Saunders from Nestle to be chief executive in 1981. Consumption of Guinness stout, the group's primary product, was sliding, and Saunders oversaw the high-profile marketing campaign that stemmed the slide.
He was also the man behind the divestment and acquisition strategy that helped to make Guinness one of the world's leading spirits groups. In 1985, Guinness bought Arthur Bell & Son, a Scotch whisky producer, and in 1986 it went after British drinks company Distillers, which was also being pursued by Argyll.
Eventually, Saunders spent nine months in jail for his part in an illegal scheme to boost Guinness's share price and enhance its position in the bid. He was released early after his attorney argued that he had Alzheimer's disease, and he is now a consultant for The Carphone Warehouse in London.
Jonathan Guinness's complicated relationship with Ernest Saunders is one of the enduring peculiarities of the entire episode. In 1987 he was the first board member publicly to call for Saunders's dismissal. Then, in 1991, he argued that "enough is enough" - it was time to let Saunders out of prison.
In Requiem for a Family Business, Jonathan Guinness takes a generally sympathetic attitude towards the man who is equally responsible for rescuing the company's profits and for tarnishing its image. He raises the question: "Was Ernest Saunders made a scapegoat?"and then answers it with an unqualified no.
"To sack Saunders without pay and in disgrace was right," he writes, before going on to ponder whether the company should have paid Saunders's legal bills. Its refusal to do so, he writes, did not "reflect the best traditions of a company like Guinness".
The other lasting consequence of the Saunders years was that, by issuing new shares to pay for the acquisitions, the Guinness family's stake fell to less than 2 per cent. Today there is not one member of the family on the Guinness board.
Since he left the board in 1988, Jonathan Guinness has kept a low profile. In 1991 he sold Obaston Hall, his 14-bedroom country house in Leicestershire, for nearly pounds 1.75m. Pushed for money, he also sold a Gainsborough portrait but complained to a journalist that most of the money raised went to pay death duties.
Apart from his three children with Shoe Taylor, he also has three children from his first wife, Ingrid, and two from his marriage to Suzanne.