DNA for the British Isles is probably the most studied of anyplace on earth.
And since it had waves of migrants, it makes for interesting speculation of what precisely took place.
Many in Britain share a DNA group which includes many from Spain, Portugal and France, indicating a probable migration by land or by sea along the Atlantic.
In any event there were pre-celts, celts, Romans, Angles, Saxon, Frisians, Jutes, Norse, and maybe others.
Those are the “coming” and many of us are the “going.”
My dad's mother (Mrs Smith) was related to Cheddar Man.