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An original sketch by Damien Hirst, which was given to a London cab driver, has sold for £12,000 at auction.

Jon Horsley, 40, from Ilford, east London, said: "I can't believe it. The bids just kept going up."

Mr Horsley's son LJ, 15, to whom the sketch is dedicated, will use the money to pursue his ambition to be a film-maker.

The scrap paper doodle of Hirst's pickled shark and jewelled skull had been expected to fetch £5,000.

Will buy camera

The sketch reached £12,000 after several lower bids at Dreweatts & Bloomsbury auction house on Wednesday.

Mr Horsley was given the drawing after Hirst climbed into his cab for a second time - the cabbie had promised his son to ask the multi-millionaire artist for a drawing if he ever picked him up again.

At the time, Mr Horsley said his son should keep the picture.

"But if it gives him a leg up with film-making it will be worth it," he said.

LJ said he hoped to buy a camera with the money earned from the sale.