Comment by tialaramex

Shots aren't necessarily 25ml, prior to metrication the legal situation had been that in England a shot was a sixth of a gill, in Scotland either a fifth or quarter depending on the establishment. The metric "Weights and Measures" legislation said each such licensed premises in the UK gets to pick, either 25ml (most common in England) or 35ml and they shall post a notice explaining to the public which volume they've chosen.

The differences in signage are because the UK's Road Traffic laws specify miles and yards still, whereas most other legislation specifies metric units, including for the waterways. So a sign legally required for an 18th century canal might say "100m" meaning metres, while an equally modern, legally required sign for a road built this century says "10m" meaning miles. This is embarrassing, but there's a strong feeling that somehow archaic unit systems are an important part of our heritage, and at least it's not as bad as when we propose getting rid of statues that celebrate slavers...