British street artist Banksy has lost a two-year trademark battle with a greetings card company over his 'Flower Thrower' graffiti work after EU officials said his anonymity meant he couldn't be identified as the owner.

The ruling by the EU's intellectual property office (EUIPO), which is based in Spain, concerns one of Banksy's most famous efforts showing a masked protester hurling a bunch of flowers, which first appeared on a wall in Jerusalem in 2005.

The mysterious artist, whose iconic graffiti paintings have appeared overnight on buildings around the world, successfully obtained a European Union trademark for the image in 2014.

But two years ago, Full Colour Black, which makes greetings cards and wanted to use the image, issued a legal challenge, claiming the trademark was taken out in bad faith as he never intended to use it for goods or services -- in a challenge accepted by the EU's intellectual property czars.

"It is clear that when [Banksy] filed the EUTM, he did not have any intention of using the sign to commercialise goods or provide services," the panel found, saying the artist's anonymity had worked against him.

Two men sit in front of Banksy's 'Flower Thrower' mural painted on a wall of a petrol station in the West Bank town of Bethlehem
Two men sit in front of Banksy's 'Flower Thrower' mural painted on a wall of a petrol station in the West Bank town of Bethlehem AFP / THOMAS COEX

"The predicament of Banksy's right to the work 'Flower Thrower' is clear. To protect the right under copyright law would require him to lose his anonymity, which would undermine his persona," it found.

"He cannot be identified as the unquestionable owner of such works as his identity is hidden."

It said he had filed the trademark in order to secure "legal rights over the [artwork] as he could not rely on copyright rights, but that is not a function of a trade mark."

Last year, Banksy opened a pop-up shop in south London, named "Gross Domestic Product", saying its purpose was to address issues raised in the dispute -- largely to show he was using the trademark, which the panel also found went against his case.

The EU panel ruled the trademark to be invalid and ordered Banksy and his legal representative to pay the costs and fees incurred by Full Colour Black. Any appeal must be filed within two months.