LONDON – In a rare and undesired appearance, “The Da Vinci Code” novelist Dan Brown dismissed as “completely fanciful” claims that he stole the ideas of two authors, saying he read their book only after the structure of his theological thriller was in place.

On Monday – three years to the week after “The Da Vinci Code” was first published – the multimillionaire writer found himself on the witness stand at London’s High Court, denying accusations of copyright infringement from Michael Baigent and Richard Leigh.

In a witness statement made public by lawyers as he took the stand, Brown said he was “shocked at their reaction” to his book. Under questioning by the plaintiffs’ lawyer, however, Brown acknowledged that he could not always recall exact dates of milestones in the creation of his novel. Both books explore theories – dismissed by theologians – that Mary Magdalene was not a prostitute but Jesus’ wife, the couple had a child and the bloodline survives.

“It’s as if you’ve asked me to go back five years or 10 years and asked me not only what I got for Christmas, but what order I opened the presents,” he told Jonathan Rayner James, a lawyer for the plaintiffs, before a courtroom packed with journalists, religious skeptics and fans.

The author, a resident of Exeter, N.H., who gives interviews only rarely, appeared composed during testimony. Only occasionally did he show impatience with Rayner James’ forensic questioning about documents and dates.

Baigent and Leigh are suing “Da Vinci Code” publisher Random House for copyright infringement, claiming Brown “appropriated the architecture” of their 1982 nonfiction book “The Holy Blood and the Holy Grail.”

If Baigent and Leigh succeed in securing an injunction to bar the use of their material, they could hold up the scheduled May 19 film release of “The Da Vinci Code,” starring Tom Hanks and Audrey Tautou.

Random House lawyers argue the ideas in dispute are so general they are not protected by copyright. They also say many of the ideas in “The Holy Blood and the Holy Grail” do not feature in Brown’s novel, which follows the fictional professor Robert Langdon as he investigates the murder of an elderly member of an ancient society that guards dark secrets about the story of Jesus and the quest for the Holy Grail.

In his 69-page witness statement, Brown acknowledged reading Baigent and Leigh’s book while he was writing “The Da Vinci Code” – along with 38 other books and more than 300 documents submitted as evidence to the court.

He said Baigent and Leigh’s work “was not a crucial or important text in the creation of the framework of ‘The Da Vinci Code.’

The statement also offered fresh insight into the creative process of one of the world’s most popular authors. His routine begins daily at 4 a.m. – a pre-dawn ritual he began when he was working two jobs as a teacher to pay the bills and the early morning hours were the only time he had.

“For me, writing is a discipline, much like playing a musical instrument,” Brown said in the statement. “By making writing my first order of business every day, I am giving it enormous symbolic importance in my life, which helps keep me motivated.”

According to the statement, the outline of the book was written in his parents’ laundry room. His desk was an ironing board.

“Because I was visiting my parents, I had no office space, and the only private place in their house was a tiny laundry room,” he said.

Brown also said he had fully acknowledged his debt to the two authors by having a character in “The Da Vinci Code” refer to the earlier book. He even named a character Sir Leigh Teabing – an anagram of Baigent and Leigh.

Other authors whose works he mentioned had sent letters of thanks, Brown said. But the plaintiffs had made allegations which contain “numerous sweeping statements which seem to me to be completely fanciful.”

The author’s statement and testimony provided tantalizing glimpses of his pre-“Da Vinci” life – from pupil at the exclusive New England prep school Phillips Exeter Academy to semi-successful Los Angeles songwriter. Brown has also written the thrillers “Deception Point” and “Angels and Demons,” both now million sellers. He has been working on a new book, again featuring Robert Langdon.

Brown’s court appearance also revealed a complex and wide-ranging research process undertaken with his wife Blythe Brown, whose interest in “the sacred feminine,” Brown said, led to one of “The Da Vinci Code'”s key themes.

Brown is due to continue his testimony on Tuesday.

The third author of “The Holy Blood and the Holy Grail,” Henry Lincoln, is not involved in the case. A lawyer for the plaintiffs, Paul Sutton, refused to say why he was not participating. Lincoln, who is in his 70s and reportedly in poor health, could not be reached for comment.