Tuesday, April 25, 2006 10:50 AM PDT

The recent proceedings at the High Court offered the first clues as to how Dan Brown produced the publishing sensation that is The Da Vinci Code.

Now the American author has offered a further tantalising glimpse into his working practices, in a talk billed as his only public appearance before the release of the film version of his novel, starring Tom Hanks, next month.

When stuck on points of the plot, Brown would dangle upside down from a pair of "gravity boots" to think it out, he told 850 people at the sell-out event presented by the New Hampshire Public Radio and The Music Hall of Portsmouth on Sunday. It was a habit adopted while figuring out anagrams for his earlier novel, Angels and Demons, he said. The bestselling author had revealed some of his unusual working methods during the recent High Court case where two historians accused him of plagiarism, a claim he successfully rebutted.

"For me, writing is a discipline, much like playing a musical instrument. It requires constant practice and honing of skills," he said.

"If I'm not at my desk by sunrise, I feel like I'm missing my most productive hours. In addition to starting early, I keep an antique hourglass on my desk and every hour break briefly to do push-ups, sit-ups and quick stretches. This helps keep the blood, and ideas, flowing."

Critics might say it explains the contortions in the plot.

With the court case behind him, Brown said he was pleased the book's mixture of religion and art history, the Knights Templar and the search for the Holy Grail, had captured popular interest. Even the Vatican had stepped in to comment, because it was unhappy about the suggestion that Jesus and Mary Magdalene had married and produced a child whose bloodline survives to the present day.

But Brown insisted that it was not his responsibility to address the controversies stirred by The Da Vinci Code.

"Let the biblical scholars and the historians battle it out," he said. "It's a book about big ideas. You can love them or you can hate them. But we're all talking about them and that's really the point of it."

The former English teacher said that he wanted to return to the classroom one day and rarely reads work he has finished - although The Da Vinci Code was an exception.

"When the galleys came back, I sat down and I read the novel start to finish in one sitting and I was really happy, really proud of it," he said.

Fans may have to wait a while for the successor to The Da Vinci Code . The new book, which will again feature the Harvard symbologist Robert Langdon as the protagonist, was expected by the end of the year. Transworld Publishers in London admitted it had hoped the book would be finished by the autumn but that it was not now expecting it until next year. "I'm in no hurry," Brown said. "I just have to write a great follow-up and it will be done when it's done."

Brown, 41, at least seemed able to laugh at his recent ordeal in the courts. "By the way, if anybody in the audience would like to sue me, we have forms out the back," he said. "Just pick one up on your way out."

Writers' habits

* PHILIP PULLMAN

Writes with a ballpoint pen on A4-sized narrow-lined paper. The paper must have a grey or blue margin and two holes. He writes only on one side and when he reaches the bottom of the page, he finishes the sentence or writes more at the top of the next so the piece of paper next morning is not blank. When he finishes a story, he types and edits it on computer.

* ROALD DAHL

Could not type and always wrote in pencil on very distinctive yellow paper. Produced most of his stories in a small hut at the end of the garden of the family home in Great Missenden in Buckinghamshire where he would sit in a wing-back armchair, his legs covered by a tartan rug and his writing board on his lap.

* ERNEST HEMINGWAY

Wrote in long-hand on onion-skin paper while standing up, until such point as he thought the work was progressing acceptably, when he would move on to his typewriter.

* VLADIMIR NABOKOV

Wrote on index cards, partly because he did not write consecutively from the beginning to the end of a chapter. He then arranged them in order and gave them to his wife to type up.