I never said metric was wonderful, just pointed out that , as others have also said, Britain mixes the 2 systems.
Not only Britain - Tyres the world over : diameter is in inches but width in mm.
I wouldn't buy a "footlong" in Subway, I wouldn't go into a Subway at all. Even if they sell the sandwich in an imperial length the nutritional information is in metric (I've just looked at their web site).
It does also work the other way around, here in the land of the Kilo it does happen that on markets you will see occasionally in season certain fruit sold by the "livre", and they don't mean by the book put by the pound, don't ask me why.