Most UK supermarkets offer this service. You need a store scanner that you pick up with the trolly. Scan everything, then pay and leave. You'll get stopped very occasionally for staff to check you aren't stealing. But they don't do much other than make you pay for things you haven't scanned. "Oh the kids put it in there without me noticing."
ASDA, at least, offer an iOS app that lets you scan as you go. Which is handy because the scanners are at the wrong* end of the store for me.
(I believe M&S has something similar?)
I've seen this at giant eagle a couple of years ago