Onlookers gasped when the then-titled Girl With Balloon was sucked into the mechanism concealed in the frame when the hammer fell. It had just sold for ￡1,042,000 at Sotheby's, London, in 2018.

       It was then renamed as Love Is In The Bin and put up for auction yesterday with an estimate of ￡4million-￡6million.

       But nine bidders battled for 10 minutes to buy it. Once the auctioneer's fees were added the purchaser, whose identity is unknown, paid ￡18.5million.

       Street artist Banksy, whose identity is kept secret, said on Instagram in 2018: "Some people think it didn't really shred.

       It did. Some people think the auction house was in on it, they weren't."

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       Sotheby's said the work fitted into an illustrious history of anti-art including Marcel Duchamp's submission of Fountain, a porcelain urinal remounted on a pedestal in 1917, to Ai Weiwei, who photographed himself intentionally dropping an alleged Han Dynasty urn.

       Sotheby's spokesman Alex Branczik said: "During that memorable night, Banksy did not so much destroy an artwork by shredding it, but instead created one.