Hi! Your post has turned into a bit of a racial debate lmao but I get how you feel, one of the reasons why I was deterred from applying to universities outside of London was because I didn't want to be in a place where I would likely be the only ethnic person in the room. But I'm currently in Nottingham and it's super diverse and I have plenty of friends from all walks of life
I'm not too familiar with the other universities, but I have a few friends in Exeter and Durham and their snapchat stories look lit
I'm pretty sure most universities have dedicated societies so even if you don't find a lot of friends in your course, you'll meet them in afro-caribbean society etc.
Also as someone who's had your exact concerns, you really have nothing to worry about, university is a huge place and it is literally impossible to not find like-minded people within the first two weeks. Also we're not living in the 1980s Britain where racism is a huge issue, us Gen Z kids are a lot more self aware about the world and we know how to poke fun at each other.
BUT, I'm not saying that your concerns are completely unfounded either. To the people saying that OP is being ignorant or whatever, Exeter faced a lot of backlash only last year for an infamous group chat where members posted insanely racist and bigoted messages:
https://thetab.com/uk/2018/03/20/named-and-pictured-the-men-behind-the-racist-exeter-group-chat-62740I've also had a couple experiences of having micro aggression thrown my way (a flatmate commenting on food from home, weird looks when you're speaking your native tongue etc) but you should understand that these are very rare and also reflect poorly more on that person than on you (I've made a lot of friends by recounting these occurrences and us having a mutual vent about how people can be so dumb in the year of our Lord 2019)
Also realistically we shouldn't expect universities to be 50-50 poc and white people because the UK itself is only 15% BAME, so you shouldn't be too surprised to meet people who may have never met a black person before, because it's really not their fault and it's a great opportunity for the both of you to learn and meet new friends
TL;DR - Don't worry about it too much OP, but if you are, Nottingham is a great place from my experience