So there we were, about to tuck into our roast lamb and all the trimmings, when right out of the blue my mother-in-law – whose birthday we were celebrating – goes and produces one of the most delightful nuggets of car info I’ve come across in many a year.

She’d heard it mentioned on the radio the day before apparently. Some chap from Which? or Wotchamaflip was being interviewed about the price of fuel, basically, and before he left the studio he said to the host; “Do you know how you can tell which side of the car your fuel filler cap is?”

To which the DJ replied, somewhat facetiously; “By getting out and having a look.”

“Nope” said Whojamawotsit. “You don’t actually have to get out of the car at all. Instead, just look at the fuel pump graphic on your fuel gauge; whichever side the pump handle sits on the gauge tells you which side of the car your filler cap is positioned.”

At a stroke, our entire family was stunned into perfect silence by this previously unknown gem of car knowledge. At which point we threw down our cutlery and, en masse, marched outside to have a look at the fuel gauges of our variously assembled cars.

A new Fiesta, a TT RS, a Golf GTi, an MGF, a Supra Turbo, a Citroen ZX Avantage and a Peugeot 207 CC were duly examined – and blow me down with a feather if my mother-in-law wasn’t absolutely spot on; whichever side the pump handle appears within the gauge itself does actually tell you which side the filler cap sits.

And if you can beat that for a small but perfectly formed piece of car trivia over your Sunday lunch, well, I’m all ears, as they say.