How can you possibly define "native Brit" in a way that includes, say, Saxons, but excludes West Africans who immigrated in the 1200s, without simply saying "pe

How can you possibly define "native Brit" in a way that includes, say, Saxons, but excludes West Africans who immigrated in the 1200s, without simply saying "people with light skin"? Or is 1066 your cutoff? Why?