A collection of attractions with an appeal to the more authoritarian side of monarchy are preparing to celebrate the coronation of Charles III with an unorthodox promotion.

The London Dungeon is offering free admission to any tourist who surrenders a copy of Prince Harry’s book Spare.

The city attraction announced the “noble gesture” as an act of loyalty to the incoming monarch.

“Spare the new monarch his blushes” urges the attraction, asking visitors to hand over the Prince’s tell-all memoir. The promotion, which brands the book as “controversial and unwanted literature”, invites the first 75 visitors to exchange their copy for free admission.

Other city attractions in the franchise, the Edinburgh Dungeon and York Dungeon, are also extending the offer between May 6 and 8.

The attractions, which focus on the more squeamish side of history, have a soft spot for the monarchy. After all, kings and queens have donated their best exhibits.

From Guido (Guy) Fawkes, who was hanged, drawn and quartered, Jacobean witch trials to Charles I, who was beheaded in Whitehall - the royals have come up with all the gory goods.

The London Dungeon attraction says the royal family and its colourful history was part of its appeal. Photo / Merlin Emtertainment

Mark Mattinson, general manager at York Dungeon told the Press they wanted to honour the King in their own way.

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 “The royal family and its colourful history has always been part of our attraction’s narrative, so it was important for us to honour His Majesty on the occasion of his coronation. And what better way than by removing all controversial and unwanted literature, keeping the streets fit for our new King.”

Of course the London Dungeon has no royal connections today… or in past days.

Having opened in the 1970s as a waxworks museum, it owes more to historic inspiration than direct royal patronage. The Merlin Entertainments-owned attraction is part of the same family as Madame Tussauds, Legoland theme park, as well as other Dungeon attractions in San Francisco, Amsterdam and Shanghai.

The less regal Shanghai Dungeon is also owned by the same franchise. Photo / Merlin Entertainment

The museum moved beneath County Hall, across Westminster Bridge on the South Bank in 2013, to be closer to other Merlin-owned attractions.

On transfer to new premises, it was discovered that one of the museum’s skeletons was real.

The Dungeon’s curators told the BBC they discovered one of the props was assembled from a “combination of some human and some artificial parts”.