The American pop star — whose real name is Katheryn Elizabeth Hudson — launched the legal action in 2009 after Australian woman Katie Jane Taylor, née Perry, registered “Katie Perry” as a trade mark.

The Australian courts initially held that while Ms Hudson adopted the name “Katy Perry” in 2002, she was not so well known by September 2008 to preclude Ms Taylor from establishing herself as “Katie Perry”.

The Federal Court of Australia has now overturned that ruling, pointing out that Katy Perry’s hit single I Kissed A Girl had been released months before Ms Taylor’s trade mark application.

The court said “die-hard fans” of the pop star “may recognise the incorrect spelling”, but an ordinary consumer “would be likely to be confused”.

Ms Taylor, who can still appeal to the High Court of Australia, said she was “devastated” by the judgment.

“It is a David and Goliath fight — and Goliath won,” she told ABC News.