Yet Mr Mantle also has a day job, writing histories for insurance companies and other businesses. His case illustrates the financial unpredictability of even a successful author, yet he is scathing of fellow authors who complain about their plight. He sees a profession that contains its fair share of the unworldly and the disingenuous.
"I would like to point out that commercial writing is a gamble. Most authors and most publishers know this, and it's a very nice way to make a living. But people tend to forget this when they are negotiating their next book. Authors are very disingenuous. It's a hangover from the late Eighties, when they were paid enormous sums for writing newspaper articles."
Most authors, he agrees, need a second job. He has been writing company histories for eight years. Yet many authors will not accept the need for a second job.
The argument over advances is, he claims, a complete red herring. "Those who complain most are the ones who are paid too much in the first place," he maintains. "But it is a red herring because the real question is how effectively they publish and market your book. It's the sales, not the advances, that make the real money." There is often no correlation anyway between advances and sales. Mr Mantle's Jeffrey Archer book had a very low advance, of pounds 3,000, yet it made nearly six figures.
"It's the incompetence of British publishers that handicap authors, not the diminishing level of advances," he claims. "My book Car Wars was published by Macmillan. During the publication process the publishers were taken over, the list was halved and I couldn't find the book anywhere. Macmillan handed me back the UK rights to the book for nothing, they were so embarrassed."
The real money, he adds, can often come off the back of successful books rather than from the books themselves. "When my books have made money, I've made far more money out of related journalism, as I am then seen as `the expert' on the subject, be it Jeffrey Archer or Lloyd's of London."
The solution to writers' financial problems does not lie in bigger advances, he claims. (Indeed the leading fiction author Brian Moore refuses to accept advances, preferring to have real income defined by real sales.) The solution, says Mr Mantle, lies in publishers becoming more efficient in the marketing of books, and in authors accepting that they will normally need other jobs.
"I'm the only known commercial author in this country who writes company histories," he says. "A lot of authors are suddenly and conveniently very unworldly."