Having lived in the UK as a (white) foreigner… You are not a whole lot better over there. “White supremacy” is a bit of a loaded term with a few different meanings. By your question, I guess you mean people who dress up in nazi cosplay? Those guys are still fairly uncommon everywhere, but the thing is that there is a porous border between your average racist prick and one of those guys. As they feel safer to express their true beliefs, they do so more often, and they want to wear the symbols of their movement. They’re very safe in the USA right now so you see more of them. But in my opinion, “white supremacy” is better used to refer to a culture which values white people more or thinks of them as higher on some kind of natural hierarchy. That is, after all, what the words literally mean. Although it’s a broader definition, I think it’s clearer, because it removes the confusion when the average racist pricks start dressing up in fash drag when someone who lets them gets into power. Explicit racists (as opposed to your normal somewhat prejudiced person who still doesn’t believe racism is good) often talk about “hiding their power level”, i.e. not letting on. What I’m saying is, the UK is similar to the US, just a bit shyer.