I was in London a few months ago. I have Android Pay (I'm American) and could use it everywhere [1]. Coffee shops, train stations, supermarkets, even a whole in a wall cafe. Unlike in US, payment simply was not a problem/point of friction at all.

I am really curious what was the thinking behind Square's UK launch (if there was). At least as a business traveler (and admittedly in London, the financial center of Europe), I saw no space in the market for Square to enter.

[1] (The ONLY place I could not use Android Pay was Apple Store)