Flats on floors in between usually have the floor number as the first part: "3FL" for third floor on the left or "2F3" for second floor, third flat. Or at least

Flats on floors in between usually have the floor number as the first part: "3FL" for third floor on the left or "2F3" for second floor, third flat. Or at least that's how it was when I lived in Edinburgh in the 90s.