I sure there are plenty of segregated places in Britain but Riz Ahmed grew up in London which is very diverse.
I was born and raised in London. A lot of film and television doesn't really reflect what modern London is actually really like in regards to the diversity and people mixing from different backgrounds.
A lot of people that aren't from the city or live here don't really understand it. Some people are scared by the cities diversity but most Londoners seem proud about it and think it is one of the things that make the city great.
There is even a social dialect called
Multicultural London English that a lot of millennials speak.
https://en.wikipedia.org/wiki/Multicultural_London_English
Eggsy from Kingsman and Ali G speak in the dialect.