CHICAGO (AFP) - The beloved British detective Sherlock Holmes is now free to be reimagined in the United States after a federal judge ruled that licencing fees are no longer required.

First introduced in 1887, Holmes entered the public domain in Britain years ago.

The literary icon has been kept alive in the public imagination with the help of scores of films - including a recent series starring Robert Downey Jr. and popular television shows like the BBC's Sherlock and CBS's Elementary.

But a quirk in US copyright law which protected ten short stories in the vast Holmes canon had allowed the descendants of author Arthur Conan Doyle to retain intellectual property rights in the United States.

A Holmes scholar challenged those fees after the Conan Doyle Estate threatened to block the distribution of a book of original short stories if the editors did not obtain a licence to use the Holmes characters.

Judge Ruben Castillo rejected the estate's claim that since Holmes and his partner Watson were "continually developed" the copyright protecting the final ten stories should extend to the characters themselves.

"The effect of adopting Conan Doyle's position would be to extend impermissibly the copyright of certain character elements of Holmes and Watson beyond their statutory period," Mr Castillo, chief justice of the northern district of Illinois, wrote in a 22 page opinion issued Monday.

Mr Castillo ruled that only the "story elements" detailed in the ten short stories published after 1923 were protected and that everything else in the Holmes canon was "free for public use." The ruling was posted Friday on a 'Free Sherlock" website maintained by the Holmes scholar, Leslie Klinger, who challenged the estate.

Mr Klinger did not immediately respond to the ruling itself.

In a statement posted when he filed the lawsuit in February, Mr Klinger said he wanted to put a stop to the estate's "bullying." "Holmes and Watson belong to the world, not to some distant relatives of Arthur Conan Doyle," he said.