Our friend the metric system
Converting between American, Imperial, and European measurements: miles and kilometers, feet and meters, pounds and kilos, gallons and liters, Fahrenheit and Celsius (plus a few others)
The British have had as contentious a relationship with adopting the metric system as the Americans—only the Brits have actually (albeit sometimes grudgingly) accepted it as the national standard over the past two decades... with some exceptions, particularly on road signs (which still use miles, yards, and mph) and in pubs (I cannot imagine a world in British pubs would serve beer by the 568.26 ml glass).
The switchover was only started in 1995, and it produced many delightfully populist news stories about "metric martyrs"—greengrocers who risked fines by insisting on selling bananas by the pound rather than the kilo, that sort of thing.
The original furor has pretty much died down, and these days you'll run into metric (sometimes accompanied by an imperial conversion) on most official signs and such—again, with the exception of road signs—while in everyday conversation, the old imperial system tends to rule (though this, too, is slowly changing).