A judgment from the trial, which is due to open next month, is expected just as the film, which stars Tom Hanks and Sir Ian McKellen, is scheduled for release on May 19.

It could set a precedent in copyright law because there is little clarity over the extent to which an author can dip into someone else’s research.

Michael Baigent and Richard Leigh, who co-wrote The Holy Blood and The Holy Grail 22 years ago, are suing Random House, Brown’s publishers, for an alleged breach of copyright of their material.

If the judge rules in their favour, the authors will seek an injunction preventing further infringement of their copyright. That would affect both the book and the film.

Sony Pictures, the studio behind the film, stands to lose millions at the box office if it loses in the High Court. The release of the film could be delayed for months and released only once the injunction is lifted. More seriously still, if Leigh and Baigent win the case they could also seek to injunct the book and the film in other jurisdictions.

They argue that Brown’s thriller, which is a story of church conspiracy and murder that has become the bestselling hardback adult novel of all time, bears undeniable similarities to events, facts and claims in their book.

They say that Brown used as his basis the “architecture” of their book — that Jesus married Mary Magdalene and had a child, founding a bloodline that was protected by the Knights Templar.

In The Da Vinci Code, Jesus did not die on the cross but married Mary Magdalene and started a family in France, where descendants of their child survive to this day. David Hooper, a lawyer specialising in copyright law, noted the irony of Baigent and Leigh injuncting the film, considering that Brown’s success has given a new lease of life to their book sales. “Why kill the golden goose? But they will have a claim on the film if they’re right,” he said.

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