It will not get that bad.
Say what you will about Western countries, but they do at least bend with enough pressure. It's been a long time coming, but it's slowly getting closer everytime they turn a blind eye to migrant ships or violent crimes
Besides, most of the violence from the yugoslav countries was driven by government-supported militias, and ALL ex-yugoslav countries had them, except for maybe the non-combatants like Montenegro and Macedonia. The UK is not in that same situation. The military would probably be appalled by the idea of turning guns on their own countrymen, even in a civil war or rebellion and especially when family members join the rebels.
The big change will probably be a right wing anti-immigration party getting elected. 50/50 on whether or not they'll actually do the deportations, and 50/50 again on whether or not they are successful in the deportations. Lots of immigrants will get away and lots of immigrants will "get away"
Aka, nothing ever happens, but real