The royal family have in recent years been at pains to point out what a scant inconvenience they are to us: their upkeep, we're told, costs each commoner just 62p a year - less than a loaf of bread. But they don't seem much of a bargain when they go and spoil your night out.
Tonight the 78th Royal Variety Performance will take place in the presence of His Royal Highness, the Prince of Wales and Her Royal Highness, the Duchess of Cornwall, to be transmitted on BBC1 next Tuesday. Ken Dodd, Take That, Barry Manilow, Meat Loaf and the casts of several musicals will feature. So what happens to the ordinary people who bought tickets for tonight's performance of a hit West End show, in some cases months ago, only to find the cast has now been commandeered.
The answer, it seems, depends on the show. The Sound of Music will go ahead as scheduled, but with Sophie Bould, who usually plays Liesl, replacing Connie Fisher as Maria, and Bould's understudy playing Liesl. The cast of Avenue Q, I hear, have brought forward curtain-up to 6pm so they can do both shows.
People who, like my family (courtesy, I should say, of my father-in-law), had tickets to see Spamalot tonight received a terse email two weeks ago informing them that the performance had been cancelled and refunding their money. Why can't Prince Charles buy his own seat instead of stealing mine?
The first Royal Command Performance was held in front of George V in 1912, ironically at the Palace Theatre where Spamalot is now in residence, and which tonight will be dark. Nearly a century on, it does seem odd that theatres and audiences are still perennially put out by this vestige of royal high-handedness. We can't blame the casts for agreeing to appear because all the proceeds go to charity (the Entertainment Artistes' Benevolent Fund), so to refuse would look callous and greedy. We can hardly blame the BBC, who fixed the recording date "according to the availability of the relevant royals", according to a spokesman, back in February. West End productions are "approached at the earliest stage" and left to decide whether to offer an alternative or to close.
This is not the biggest injustice to result from living under a monarchy, just another small grievance to add to the list. No hard feelings, Charles. Enjoy the show; see you next Tuesday.