True. Otherwise we would be using square meters for measuring gas mileage instead of miles-per-gallon (or litres-per-km) [1].

[1] https://what-if.xkcd.com/11/

Well, if you want to be pedantic, it's litres-of-fuel per km-driven. That doesn't cancel as nicely, if you don't drop the annotations.

Arguably, we should probably use kg-of-fuel (or mol) instead of litres-of-fuel anyway.

> miles-per-gallon (or litres-per-km) [1].

The UK is metric except for distance and beer.

So the disgusting ‘miles-per-litre’ is presumably needed too.

Also the UK gallon is different from the US gallon. And the same applies to all the other non-metric fluid measurements such as pints and fluid ounces. Historically the UK gallon was used throughout the former British Empire (Australia, Canada, India, Ireland, Malaysia, New Zealand, South Africa, etc). By contrast, almost nobody ever officially used the US gallon except for the US (and a small handful of highly US-influenced countries such as Liberia).