Those meeting the Queen are barred from talking about a certain topic of conversation, reports said.

The guests of the 93-year-old monarch were advised not to speak about Prince Harry and Duchess Meghan, a royal source told The Sun.

“Courtiers were aware the Sussexes are all anyone wants to ask her about,” the source said.

“So to nip it in the bud, some have taken to having a quiet word with some guests awaiting an audience with the Queen. They suggested that questions around Harry and Meghan may not be the best choice as a topic of polite conversation. Naturally, it’s informal rather than any official policy and there’s no suggestion the Queen is even aware.”

Journalist Quentin Letts also wrote on Twitter that he heard accounts of the advice being proffered to the Queen’s riding guests.

“Friend of an acquaintance was about to go riding with HMQ [Her Majesty the Queen],” he wrote. “Was given v firm advice. ‘Talk about anything except one subject.’ ‘Brexit?’ ‘No. The Sussexes.’”

In April, the Duke and Duchess of Sussex moved into the Frogmore Cottage to become the neighbours of the Queen, who live in the nearby Windsor Castle.