Hogwarts aficionados will notice that both exhibition and book are structured according to the School of Witchcraft and Wizardry’s curriculum – potions, charms, divination, care of magical creatures and herbology. There are mermaids and unicorns, brooms and cauldrons, spells and oracles. And everything has been painstakingly matched to its appearance in Potter.

Harry learned to “unfog the future” in Sybill Trelawney’s divination class, and a flock of objects pertaining to this ancient art have been unearthed. Crystal balls used during the 19th century, a scrying mirror belonging to Cecil Williamson, the British witch, and a collection of Chinese oracle bones, used 3,000 years ago to allay concerns about war and harvest. Even the characters are rooted in reality. Nicolas Flamel, the 665-year-old alchemist Hermione identifies as “the only known maker of the Philosopher’s Stone”, is based on a bookseller of the same name who lived in 14th-century Paris, and whose experiments in transmutation – turning metal into gold – were known to Sir Isaac Newton. For the exhibition, Flamel’s tombstone has been brought all the way from Paris.

Many items are presented alongside ancient manuscripts or paintings – a painting by John William Waterhouse from 1886 of a witch and her smoky brew appears with a cauldron from the Museum of Witchcraft in Boscastle. It’s powerful iconography that has lasted for centuries – in The Chamber of Secrets, Hermione “feverishly” stirs a cauldron of her own.

While many of the objects now seem quaint or hare-brained, plenty remain able to raise hairs on the back of your neck. A spell for invisibility (reproduced in the book, should you wish to try it), and a “real” mermaid donated to the British Museum in 1942. In fact, the latter was part of a colossal trade in 18th century fakery, produced in Asia and designed to ornament European drawing rooms. Created by sewing the torso of a monkey on to the tail of a fish, it is possibly even more gruesome than the merpeople of The Goblet of Fire, whose “greyish skins and long, wild, dark green hair” so terrified Harry.