Create a new black death which affects only people with high levels of melanin
What should you do? its a bit too late to ask that dont you think? No way this could be good, ilegal migration is never good. Leftism has taken over schools, universities, media and politics... You would need strong leaders to solve this matter, you have a tough task right now. Either islamic culture or western culture will prevail, and right now islamic culture is prevailing thanks to cultural marxism.
Statistically there is no correlation between the % of white British and crime. Crime was higher when we had a much higher percentage of white British in London. In fact 2013/14 was our lowest crime in London in several decades. The cuts to policing and other social things have recently increased crime.