When more people shared a common cultural history it becomes easier to have an understanding from the other person's view.
Problem is that parts of the UK are very multi-cultural, and many of those communities prefer to keep their previous cultures.
What shared cultural history is there when you have a local community that has people form India, Pakistan, Bangladesh, UK, Russia, Ukraine, Hong Kong, China, Singapore, Poland, Romania, France, Spain, Turkey, and so on, parts of Africa, etc.
You can "maybe" have some common European culture between the UK + western EU groups, maybe common British culture between the UK and GK groups, but how do you find a common culture across all these groups?