I was in England for four months. Milk and water were sold by the liter, which took some getting used to. I think speed limits were still in miles per hour, but as I obviously didn't drive, I don't remember with any certainty. (You know what's a real affront to social harmony? The British drive on the wrong side of the road.)
Milk sold by the litre? I don't think I've ever seen that before?
I'm pretty sure it's by pints, unless it depends on the brand of milk you buy.
Hmm, I thought it was in mL. But maybe I misremember, as this was almost a year ago. I was just shopping at Tesco and Sainsbury's, so it wasn't anything exotic.
All I know for sure is that the jugs did not look like the familiar (U.S.) sizes.