What is British?
How far back do we go to get to a true British identity?
The first Britons were immigrants. They had a Neanderthal level of intelligence. They died out about 30,000 when they were out-foxed by smarter, lighter, African migrants.
The second Britons were also immigrants. They were so primitive they couldn't even make a decent stone arrow. (I've tried, it's damned hard). They left again when it got too cold to hunt woolly rhino.
The third Britons were pretty good at stone arrows, and other stone tools. They even learnt to farm and domesticate animals. At this point, history becomes a bit hazy, but the next lot we know about came from Italy. Then came the Angles, Saxons, vikings (Danes), Normans (who also were Danish via France, which was British half the time). Then things settled down a bit, and economic and social migration became the norm. Of course, the ruling class still had it's mix-ups, Half the time Britain was a French colony, and half the time the other way round. Not that it made much difference to the peasants. When we got a bit short of 'native' royalty, we ended up importing it from Scotland, France, Germany.
When the Empire got a bit shaky, we invited a lot of the previous slaves or colonials to come and do the hard work, and they did, and mostly worked very hard at it. A lot of these are now very well established in the family trees of our aristocracy if you look carefully.
Britons are mongrels. We should be proud of it.