> almost no one in UK accepts signature-only cards

> terminals which can take magnetic-strips are just super rare and usually not supported even if the machine has them.

I've not found this to be the case. I used a non-chip US card here in the UK extensively over the last year or so, and I've never once encountered a merchant that didn't want to take my card, nor a terminal that didn't read magnetic strips.

I do find people at checkouts to be a little surprised by someone having to swipe & sign, since that's quite rare now. And often they had trouble finding a pen for me to sign with :) But I was always able to complete the transaction nonetheless.