The British publisher of J.K. Rowling's Harry Potter series is blasting plagiarism allegations about the blockbuster books as "unfounded, unsubstantiated and untrue."

The estate of author Adrian Jacobs, who died in 1997, has filed a suit against Bloomsbury Publishing in the U.K. that accuses Rowling of borrowing ideas for her boy wizard series.

The suit alleges that elements from Rowling's fourth book — Harry Potter and the Goblet of Fire — copied elements from the 1987 Jacobs book The Adventures of Willy the Wizard - No. 1 Livid Land.

According to the suit, similar elements include a wizard competition and wizards travelling by train.

"Both Willy and Harry are required to work out the exact nature of the main task of the contest, which they both achieve in a bathroom assisted by clues from helpers, in order to discover how to rescue human hostages imprisoned by a community of half-human, half-animal fantasy creatures," the suit says.

Bloomsbury described the 1987 book as "a very insubstantial booklet running 36 pages, which had a 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."

The publisher added that lawyers acting on behalf of Jacobs's son first brought the lawsuit five years ago — after the Potter series had become an international success selling millions around the globe and spawning a hit film franchise.

"This claim is without merit and will be defended vigorously," Bloomsbury said in a statement on Monday.

Rowling "had never heard of Adrian Jacobs nor seen, read or heard of his book Willy The Wizard until this claim was first made in 2004, almost seven years after the publication of the first book in the highly publicized Harry Potter series."

With files from The Associated Press