It is one thing when a TV crew lets the odd anachronism creep in. But when a real countess can't get things right, well, it's enough to make Violet Crawley choke on the hors d'oeuvres.
The countess in question is Lady Fiona Carnarvon, of Highclere Castle, Berkshire, which is better known as the location for Downton Abbey.
After speaking out about mistakes the production company made when laying the table, the last thing Lady Carnarvon expected was to have her own sense of etiquette questioned.
Her original worry concerned misplaced wine glasses. "Glasses [were] back to front and things set wrong … I try not to look because it's easier."
But Lady Carnarvon found herself out of her depth when she joined a dining table with the self-styled etiquette expert William Hanson on The Alan Titchmarsh Show.
Shown some antique cutlery, her first mistake was to express surprise at how big the spoons were, only for Mr Hanson to retort that old-fashioned spoons were much bigger than modern equivalents.
She was next pulled up on butter knives, which she and Titchmarsh both felt should sit on top of the bread plate. Not so: Mr Hanson assured them that it was placed to the farthest right of all the other knives.
As for placing pudding spoons above the dinner plate, well, that was a crass US import: English stately homes would have had a crescent-shaped salad dish above the plate.
Mr Hanson's final words of advice were on bananas. "You couldn't just have eaten [them] like a primate," he said. "You've got to peel it and eat it with a knife and fork."
Here, at least, Lady Carnarvon, who lives with her husband, the 8th Earl, at Highclere, could stand up for herself: "I would never eat a banana like this," she protested, before adding: "But I would never serve you a banana."
The fourth series of Downton Abbey starts tonight at 9pm on ITV1