My S7 installed the app automatically when it upgraded the firmware few days ago.
Haven't used it or Android Pay yet, (within the past 2 years my credit and debit cards expired, the new cards the bank sends me are never contactless so I've still been using chip and pin. I don't know why they hate me.)
Does the UK get those fancy free money rewards the OP is on about? I might give it a go if they do.
I have no idea.