I've lived in London for 22 years, coming from a rural town in Northamptonshire. Northants is now more diverse than it was, but nowhere near as diverse as the capital.
I admit, I have made assumptions about people in the past. They correct me, I say I am very sorry, and remember to not be an ass the next time. I have also read a lot about different cultures over the years.
The cleaners at work are Bulgarian, Lithuanian, and Romanian. All are very hard workers, and all lovely people. I work with Africans, Pakistanis, West Indians, Filipinas, Indians, Chinese, all religious or not.
My workplace is hot on racism and prejudice, so I think it comes out more implied than explicit. For example, my Pakistani colleague was being given all the shitty jobs to do by an Indian manager, until they asked wtf they're problem with them was?
In wider society, there are prejudices. I have been called Honky by an African before (I'm white) and during the course of my job, by upholding the rules, some customers call me a white bitch or white whore.
Racism towards eastern Europeans is rife in London, along with towards Jews and to a lesser extent, Irish. More wealthy whites treat Eastern Europeans like absolute shit, especially if they are caring for their kids or serving them food.
My step-MIL has called black people "coloured" and I have said, no, don't say that. She always looks confused when I say that. Why has she not learned? My parents are racist. They deny my neice and nephew's black WI heritage and are always going on about Eastern Europeans coming over and taking people's jobs. They are both retired now and go to establishments run by Eastern Europeans though. I ask them, would you like to do their jobs? Of course not, they say. I don't get it.
I am ashamed of this country's colonial past and I don't think enough British white people know about the harm we did around the world, some of which we still see today. We still have this attitude that our culture, values, religion, and constitution trump most others in the world. It's arrogance. It forms the idea that some people are "less" than us. I don't think that some white British people have evolved for decades. I voted Leave in the EU referendum not because of immigration, or law, or funny shaped veg, but because the EU is mostly undemocratic and it costs vast amounts to belong. My parents voted leave to stop the Romanians coming in.