He is perhaps best known for his carefully guarded anonymity, but Banksy has this week discovered that the Oscars do not "do" enigma. The British street artist has been refused permission to appear in disguise at Sunday night's Academy Awards, where he is up for best documentary for his debut feature film, Exit Through the Gift Shop.

Bruce Davis, the Academy's executive director, said it had been forced to turn down the request due to fears impostors would attempt to gatecrash the ceremony.

"The fun but disquieting scenario is that if the film wins and five guys in monkey masks come to the stage all saying, 'I'm Banksy,' who the hell do we give it to?" he said.

When his nomination was announced, Banksy called it a "big surprise."

"I don't agree with the concept of award ceremonies, but I'm prepared to make an exception for the ones I'm nominated for," he said, adding: "The last time there was a naked man covered in gold paint in my house, it was me."

The artist now seems unlikely to appear at the ceremony at the Kodak Theatre in Los Angeles, though reports suggest he will be in the vicinity. A number of new graffiti pieces have appeared in the city over recent weeks, including one of Peanuts's Charlie Brown pouring petrol on the side of a burned-out building.