The biggest difference between the UK and the US is the customer service culture. In the US staff are much more attentive and deferential than in the UK. My US friends were pretty horrified by the 'surly, uninterested' staff they met in shops over here while I was completely overwhelmed and freaked out by the 'intrusiveness' of US staff. (Those are perceptions and deliberately hyperbolic, not insults by the way!)
I always liked shopping in England. I found the employees to be friendly, but not overbearing. I don't mind friendly American store employees, but I really don't want all six of them asking me if I need any help, and can they help me find my size in something, and do I need a basket? Sometimes, you can't see the clothes for all the employees in the way
Once, when I was living in London, I bought a bottle of wine with my groceries. I was, I think, 19 at the time, so legal there, but barely. The poor cashier seemed terrified to ask me for my ID. I got the impression that her customers were not a fan of being carded, whereas for me, it was a totally normal thing. Of course you're going to be carded if you're within a couple years of legal drinking age! She was so timid about it. I mentioned it to friends later, and I guess carding isn't common in England. I must have looked particularly young, for her to take the risk
As an interesting contrast to the detached/aggressive store clerks, I was surprised by the public transportation employees in London. At home in Chicago, you get a range from friendly enough if you approach them first to surly jerks. I was in the underground one day in London, looking sort of like I didn't know where I was going (because I didn't), but not in a terribly lost, panicky way (the area was unfamiliar, but there were signs and such, and I'm good with figuring out foreign subway systems). A very friendly employee actually approached me out of the blue and offered help. It surprised me, and I think of it every time people complain about surly public transportation workers in England. Of course, for all I know, she was the one rare exception. My future tube experiences were fairly hands off.