Harry Potter: How many wizards live among us?

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Can the number of people who use amenities such as shops, schools and a hospital in the UK help presenters Tim Harford and Lizzy McNeill come up with the number of wizards living in the UK and Ireland? The team take clues dropped by JK Rowling, the Harry Potter books and 'amenity ratios' to make their calculations. Photo: Hogwarts in the Wizarding World of Harry Potter, Universal Studios Credit: Getty Images