[icegreentea2]

UK uses "imperial gallons", which are no more metric than US customary gallons. Expanded to 3 decimals, a UK/imperial gallon is 4.546L, and a US customary gallon is 3.786, and a US gallon is close to 3.8L, than a imperial gallon is to 4.5L.

[testing22321]

I’m Australia we always call the 4.5 one a “metric gallon”