My apologies if I am not explaining properly - I will try to be as concrete as possible. I realize my perspectives are a little different from yours, which is likely why immigration policy seems like an unrelated topic.
If the majority of white British are not comfortable with current immigration trends, this also suggests that there is likely a problem with having so many immigrants in the UK. One cardinal issue is the fact that many British feel that UK just isn't "British" anymore, as more immigrants from Eastern Europe and Asia pour in. As a result, when the British people are not having their opinions heard by the government officials, who continue to bring in more foreigners, it is most certainly seen as an act of aggression by the minorities, who don't seem to be hearing their perspectives on wanting to live in a culture they grew up in, and feel comfortable in. Thus, this prompts white flight.