Harry Potter author JK Rowling may have to defend herself at the High Court against an allegation of copying her ideas from an earlier obscure children's book writer.
Mr Justice Kitchin ruled today that the claim by the estate of the late Adrian Jacobs had a chance of success but this was "improbable".
He refused applications by Ms Rowling and her publishers, Bloomsbury, for an immediate judgment dismissing the case as having no chance of success.
But he ordered that Paul Allen, the estate's trustee, pay money into court as security for the costs of the case if it goes to trial.
Mr Jacobs wrote what the judge described as a "16-page novella" entitled Willy the Wizard and Mr Allen claims Harry Potter and the Goblet of Fire infringed the copyright.
Ms Rowling and her publishers say the books are not similar except at the most generalised level and those similarities had happened by chance.
The Potter author said she had never heard of Willy the Wizard or Mr Jacobs before the publication of the Goblet book.
Mr Allen is claiming that there is substantial evidence to show that Ms Rowling's claims that she did not have access to Mr Jacobs's book before she wrote Goblet are untrue, said the judge.
Willy the Wizard was published in 1987. A year later Mr Jacobs was declared bankrupt and died in 1997.
Mr Allen claims that in 1987, Christopher Little, who became Ms Rowling's literary agent some eight years later, was given copies of Mr Jacobs's book and that he gave one to Ms Rowling before she wrote Goblet or any of the Harry Potter books.
Ms Rowling is claiming she did not meet Mr Little until 1995 by which time she had written Harry Potter and the Philosopher's Stone and the other books had been planned.
She says she did not see Willy the Wizard until 2004 when the first of the copyright infringement claims were made.
Ms Rowling has described the claim as "not only unfounded but absurd".
Mr Little described Willy the Wizard to the judge as "an appalling book" and that Mr Jacobs had never given him a copy.
The judge said: "Plainly these are disputes which I cannot resolve upon this application. But the evidence to which I have referred raises a real possibility that Mr Little's account of events is simply not correct."
He said he found Ms Rowling's evidence "very powerful" and Mr Allen had nothing with which to challenge it.
Both Ms Rowling and her publishers had told the judge that behind Mr Allen's allegation "lies a consortium seeking to use this claim to extort a settlement from the defendants and sell more copies of Willy the Wizard on the back of the publicity it generates".