The estate of a bankrupt Jewish author who died in London over a decade ago is at the centre of a "billion dollar" copyright case against JK Rowling.

Adrian Jacobs, a lawyer and accountant who made millions on the stock market before going bust, wrote a children's book in 1987 entitled The Adventures of Willy the Wizard No. 1: Livid Land.

Lawyers for his estate last week added the name of the multi-millionaire Harry Potter author to a lawsuit it filed in the High Court last June - 12 years after Mr Jacobs died in Nightingale House, the south London home for elderly Jews.

The suit claims that Ms Rowling plagiarised ideas for her fourth book, Harry Potter and the Goblet of Fire (2000), from Mr Jacobs's book.

Ms Rowling, who is worth almost £500 million, blasted the allegations as "unfounded" and "absurd". She said: "I am saddened that yet another claim has been made that I have taken material from another source to write Harry.

"I had never heard of the author or the book before the first accusation in 2004; I have certainly never read the book. We will be applying to the court immediately for a ruling that the claim is without merit and should therefore be dismissed without delay."

Max Markson, the Bournemouth-born, Sydney-based publicist for the case, says the estate has taken the case to the High Court because Ms Rowling's publisher in the UK, Bloomsbury, had repeatedly rebuffed the allegations.

"It has the same plot line, everything that's in Willy the Wizard is in The Goblet of Fire," Mr Markson told the JC.

Mr Markson was a student at Carmel College between 1966 and 1972 before moving to Australia. He said that his older brother, David, who had also written a book, was "very, very close" to Mr Jacobs and had introduced him to his literary agent at the time, Christopher Little, who now acts for Ms Rowling.

"In 2003 the connection was made that Christopher Little, Adrian's agent, was now JK Rowling's agent and that's when we started looking into it more," Mr Markson said.

Mr Little denies acting for Mr Jacobs, although Mr Markson said there was a witness statement to the High Court showing otherwise.

In 2004, lawyers for Mr Jacobs's son Jonathan, who lives in America, first approached Bloomsbury with allegations that Ms Rowling had pilfered ideas from Mr Jacobs.

Max Markson said: "It's a billion-dollar case, it's in the High Court of England. It doesn't get much bigger."