ACTION THRILLERS, whopping great doorstops with gold writing on the covers, are not only big books, they are big business.

When James Patterson, author of the Alex Cross series, produces a new book, 1.25 million copies are routinely printed. After he was poached from Headline by Random House last year the victors crowed: “Signing James Patterson is like acquiring a one-man publishing industry.” His fortune was estimated by Forbes to be $28 million (£14 million) in 2005. Another big name, Robert Ludlum, has 210 million books in print, and every one of his titles has been on The New York Timesbestseller list. Clive Cussler has 70 million copies of his Dirk Pitt series in print, and Penguin UK sells 700,000 of his books every year. The books are fast-paced and addictive and readers cannot get enough of them. Including paperbacks, Cussler alone has five books out in the UK this year and each one is a guaranteed bestseller.

Small wonder, then, that the production of so many page-turners involves more than lone writers toiling in garrets. More and more, the people producing million-sellers are leaning on collaborative authors to do much of the writing.

The authors’ names still appear on the covers in 3in-high letters, but what we’re buying is the brand, not the writer. Robert Ludlum produces several books a year, every one a bestseller — and he died in 2001. More than a dozen books have been published with his name on the cover since, including the Covert-One series, none of which appeared during his lifetime. Readers aren’t worried, and continue to buy hundreds of thousands of the books.

Thriller writing does have a long history of collaboration. Twenty years ago Patrick Larkin was writing thrillers with Larry Bond, including The Enemy Within, but, as Larkin says: “In those days, it was quite unusual to have two names appearing on the front of the book, so Larry’s name went on.” Crucially, however: “We split the money right down the middle.” But today’s collaborations differ in a number of ways. First, they are no secret — James Patterson recently gave an interview alongside one of his collaborators, Michael Ledwidge. The names of the co-writers appear on the covers, sometimes in rather small writing, but not always. And, unlike Larkin and Bond, the money might not be divided equally. (Patterson refused to elaborate on this in a recent interview, but insisted that all parties were satisfied.) Also, while the co-writers have much to do in the way of knocking out the words, they might have less creative input than when Larkin was writing collaboratively. Then, he says, the process went like this: “We would spend a few days beating out the plot together. We would write a very detailed outline, 30 or 40 single-spaced pages with characters and battles. Once we had that, I would go back home.

“Then we could write whole chapters, or whole stories of a particular character, by ourselves, and send it to the other person for tweaking. Fortunately e-mail came along early in the writing process, and we could make changes pretty quickly.”

One of Patterson’s regular co-au-thors, Maxine Paetro, reveales a a rather different working relationship today. “Jim comes up with the story idea,” she says. “It’s pretty densely written and about 30 pages long. He sends it over to me for a month or two, while I think about it and come up with ideas. I add my two cents worth, and send it back to him. Sometimes he will say: ‘Maxine, that’s fantastic,’ which I love, but other times he says: ‘This isn’t how I tell stories’. ”

Patterson is renowned for his “golden gut”, an instinct for what will and won’t work in a story. When Paetro receives the final outline, conceived by Patterson and worked on by her, she fleshes it out into a manuscript, which will become a 400-page book, and hands it over to him. “And it’s his book,” she says. “He runs with it from there, although he won’t usually make big changes.” When Larkin worked on the posthumous Robert Ludlum series, the brief was even more specific. The editors suggested a plot outline, and the deadline was so tight that Larkin had little time to worry too much about getting the voice just right.

This conveyor-belt form of writing may seem restrictive but the writers seem to enjoy it. Paetro says: “It is a lot of fun. It is much less lonely than writing for months with just me and my cat and it’s wonderful to have feed-back from a master storyteller.” Patterson, meanwhile, was once subjected to a quiz on television where he was asked to identify his own books from sections read out from them. He failed, but remained cheerful, as well he might. This is a man who has sold more than 100 million books to readers not too bothered that he doesn’t craft his own sub clauses.

This is the ultimate in commercial fiction. When readers see a famous name on a book jacket, it does not tell them that the author has written every word in the book, but that someone has ensured that they will get the product they are expecting. Rather than waiting a year for a book genuinely written by the author, the sales figures show that readers are only too grateful to the co-authors for giving them their fix of thrills and spills several times a year.

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