The alleged assault took place while Charles, 74, who came to the throne in September after the death of his mother Queen Elizabeth, was visiting Luton, northwest of London.

A police spokesperson confirmed a man in his 20s had been arrested in Luton’s St George’s Square and was in custody for questioning.

PA Media reported the King was temporarily steered away from the crowds outside Luton Town Hall by his security staff shortly after arriving.

He then resumed shaking hands with members of the public after being moved to a different area.

Buckingham Palace declined to comment.

Last month, a man was detained by police after eggs were thrown at Charles and Camilla, his wife and the queen consort, as they carried out an engagement in northern England.

The latest incident comes as the royal family braces itself for the release of a Netflix documentary series on Thursday about the king’s younger son Prince Harry and his wife Meghan.

It also comes a week after the royals became embroiled in a race row involving the godmother of Prince William, the King’s eldest son, who left her honorary role after making “unacceptable” comments about race and citizenship to a guest at a Buckingham Palace function.

Egg protests are not a new occurrence for the royals: eggs were thrown at Elizabeth’s royal car in 2002 when she visited Nottingham, central England, and anti-British protesters threw eggs at Charles during a walkabout in central Dublin in 1995.

-with PA