London ? It’s the latest twist for the mega-selling conspiracy thriller “The Da Vinci Code”: a lawsuit against the book’s publisher for breach of copyright that could taint the novel and delay the much-anticipated movie version.

Michael Baigent and Richard Leigh, authors of the 1982 nonfiction book “The Holy Blood and the Holy Grail,” are suing publisher Random House, Inc. over the allegation that parts of their work formed the basis of Dan Brown’s novel, which has sold more than 40 million copies worldwide and remains high on best seller lists nearly three years after publication.

If the writers succeed in securing an injunction to bar the use of their material, they could hold up the scheduled May 19 release of “The Da Vinci Code” film, starring Tom Hanks and directed by Ron Howard.

Brown, who rarely speaks to the media, sat attentively before a judge in London’s High Court, a short walk from Temple Church – the place of worship founded by the Knights Templar – which figures in his novel. A New Hampshire native who still lives in his home state and has been working on a new novel, Brown is expected to give evidence here next week.

Brown, was “interested in taking, and took, short cuts rather than doing any of the work himself,” Jonathan Rayner James, lawyer for Baigent and Leigh, told the court.

Baigent, born in New Zealand, and Leigh, originally from the United States, are suing Random House, which also published their book. The company denies the claim and chief executive Gail Rebuck said in a statement that she believed the lawsuit was without merit.

Michael Baigent, co-author of the book 'The Holy Blood and the Holy Grail,' arrives at the Royal Courts of Justice in London for a legal case taken out against author Dan Brown, author of the book 'The Da Vinci Code', Monday Feb. 27, 2006. Lawyers acting for the two authors of 'The Holy Blood and the Holy Grail,' a nonfiction title that suggested Jesus fathered children and didn't die during the Crucifixion, claim writer Dan Brown of 'The Da Vinci Code' stole their carefully researched arguments to weave into his fictional best-seller narrative. The writers' civil action against publisher Random House, said their book is one of at least 10 source texts Brown consulted, but said he had a heavy

Both books hinge on the theory that Jesus married Mary Magdalene and they had a child, and that the blood line survives to this day. The earlier book set out the notion that Christ did not die on the cross but lived later in France.

James said his case was not attempting to “stultify creative endeavor,” or to claim a monopoly on ideas or historical debate, but to prove that Brown had “relied heavily” on the earlier work, published in Britain in 1982 and the following year in the United States.

Though it does not relate to theft of specific sections of text, the case involves the alleged appropriation of themes and ideas from the earlier work, James said.

Brown’s wife, Blythe Brown, and Ohio University librarian Stan Planton scoured religious and historical texts on Brown’s behalf as he wrote his novel, typing up notes and in some instances, copying parts of the 1982 book, James said.

The extent of “highlighted markings” in Blythe Brown’s copy of “The Holy Blood and the Holy Grail” show it was not “merely consulted as an incidental reference source,” James said.

“The markings are far more extensive and detailed than in any other book,” he told the court.

Phrases used in both books to describe arguments that Jesus had been married showed similarities, James said. He told the court Brown’s work also appeared to reproduce “unusual and unlikely” connections between historical and religious figures set out in the earlier work.

Brown has denied claims that he reproduced sections of argument from the 1982 book and said he disputes the proposition it makes that Jesus did not die on the cross.

“This is not an idea that I would ever have found appealing. Being raised a Christian … I’m well aware that Christ’s crucifixion is the very core of the Christian faith,” Brown told reporters outside the courtroom, referring to the argument in the 1982 book that Christ had not died.

Brown’s book also was the target of a previous lawsuit. In 2005, a U.S. judge ruled that his book did not infringe on the copyrights of “Daughter of God,” by Lewis Perdue. The judge also ruled out any copyright violations of Perdue’s 1983 novel, “The Da Vinci Legacy.”