Overheadsmash, I understand you wanting to ask these questions before a life-changing move. The unknown is always scary. My advice would be to ask away before you leave, but please don't arrive with a ready-formed opinion based on what a few strangers on the Internet have told you about their experiences!
Just like the US, some areas of the UK are more cosmopolitan than others. Just like the US, there are people who have funny ideas about foreigners (from any corner of the world). Most importanly, just like the US, every person is an individual who has watched different movies, travelled different amounts and read different newspapers in their lifetime.
Be open and ready to have some of your ideas reinforced and some challenged. Unless you spend your entire life in the place where you grew up, this will happen anywhere, anyway!