As a mechanical design engineer in America having dual systems creates unnecessary complexity and frustration and cost for me all day every day. I full force embrace switching to metric
as a mechanic working in a hodgepodge US/EU factory line, I have to suffer through always carrying double the tools to service metric and SAE machines. and after so many years in the industry, I still slip up and say 3/16 when I mean 3/8 sometimes, because fractions are a shit system for wrenches.
oh, and some of our linear encoders readout decimal-feet, because fuck it, why not?
My condolences. I'm already annoyed with the times USC units are presented in Australia (our nominal pipe sizes are often talked about in inches, and sometimes valves and such have USC flow coefficients because the manufacturer is American).
So I cannot imagine the pain you must be subjected to.
There are three sizing standards used in the UK right now: metric for newer homes, imperial for older homes and farmer's sizing for fuck you, that's why.