I think GS just hit the nail on the head. It should be taught, but for legacy / historical reasons. Imperial measures do still crop up occasionally, road signs being the obvious one, and pints in a pub, so it’s a “nice to have” in the same way as, oh I don’t know, a smattering of Latin perhaps. I’m struggling to see any compelling reason to teach it as a primary system of measurement.
There’s not a lot of UK Imperial measurements left in common usage. Road signage is the obvious one. I’d still describe my height and weight in feet and stones, but there’s no real need for that other than habit and it’ll die out of its own accord as my generation, well, die out.
I started school in the 70s in the wake of the metric system being introduced so have the dubious benefit of using both systems fairly interchangeably (and sometimes simultaneously – I’m quite happy to measure something as “eighteen inches and 5mm”). CMD is 47, I can only assume that he was originally taught Imperial and then Metric later as it was phased in. It seems… weird to me to be seriously suggesting it in schools, maybe he is just on the wrong side of being too old to have fully adopted it?