Publishers could face legal action worldwide over claims that JK Rowling stole ideas for Harry Potter from a British author's book called The Adventures of Willy the Wizard.
The estate of the late Adrian Jacobs yesterday added Rowling as a defendant in a case originally filed in June against Bloomsbury Publishing, Potter's UK publisher, for alleged copyright infringement.
Max Markson, a PR executive representing the estate, told the Guardian the addition of Rowling's name to the action opened up the possibility of multi-jurisdiction action.
"We believe that she [Rowling] personally plagiarised the Willy the Wizard book. All of Willy the Wizard is in the Goblet of Fire. We now have a case which is not just against Bloomsbury."
Markson, who was a friend of Jacobs, said Rowling was added to the lawsuit after it was learned that the statute of limitations to sue her had not run out as previously thought. She is named in the suit under her married name of Joanne Kathleen Murray.
"I estimate it's a billion-dollar case," Markson said. "That'll be the decision of the courts, obviously."
Rowling denies the claims. "I am saddened that yet another claim has been made that I have taken material from another source to write Harry. The fact is I had never heard of the author or the book before the first accusation by those connected to the author's estate in 2004; I have certainly never read the book," she said in a statement.
"The claims that are made are not only unfounded but absurd and I am disappointed that I, and my UK publisher Bloomsbury, are put in a position to have to defend ourselves. We will be applying to the court immediately for a ruling that the claim is without merit and should therefore be dismissed without delay."
The suit claims Rowling's book Harry Potter and the Goblet of Fire copied substantial parts of Jacobs' 36-page book The Adventures of Willy the Wizard – No 1 Livid Land. The plagiarism claims stem from both Willy and Harry being required to solve a task as part of a contest, which they achieve in a bathroom assisted by clues from helpers.
Jacobs' estate also claims that many other ideas from Willy the Wizard were copied into the Potter books. Goblet of Fire was the fourth book in Rowling's series and was published in July 2000. No 1 Livid Land was published in 1987.
According to Markson, Jacobs had sought the services of the literary agent Christopher Little, who later became Rowling's agent.
Jacobs was a solicitor and accountant who lost heavily in the 1987 stock market crash. He suffered a stroke soon after and was bankrupted for a second time in 1991. He died in a London hospice in 1997, Markson said.
"Willy The Wizard is a very insubstantial booklet running to 36 pages which had very limited distribution. The central character of Willy The Wizard is not a young wizard and the book does not revolve around a wizard school," Bloomsbury said last year.
"The claim was unable to identify any text in the Harry Potter books which was said to copy Willy the Wizard."
Markson said the plagiarism allegation concerned the story plot rather than the words. The Jacobs estate is seeking legal advice on whether the Harry Potter films and soon-to-be-opened Harry Potter theme park breach copyright law.
In 2007 Rowling and Warner Bros, which made the Potter films, sued the publishers of the Harry Potter Lexicon, an encyclopaedia of the series. A shortened and modified version of the lexicon was published last year.