He spotted the potential of J K Rowling’s first Harry Potter manuscript, signing her up before warning her she ought to get a day job because she was unlikely to make money out of children’s books.

But no man could be more delighted to be proved wrong than Barry Cunningham, the editor, who will next month make a fortune after selling his unique bejewelled copy of a rare Potter book at auction.

Cunningham, a father-of-six, is to sell his one-off edition of The Tales of Beedle the Bard at Sotheby’s with the blessing of J K Rowling, nearly 20 years after Harry Potter first hit the shelves.