"Britain is basically the same people."
Not exactly true!
Britain's modern derived population base is fairly diverse: Celts/Druids, Roman/Latin, Angles, Saxons, Norse, Gaulic/Norman/French... and, since Victorian times legal immigration from the (now former) 'over-seas possessions': South Asia (India/Pakistan/Bangladesh), South Africa, Caribbean territories, Canada, the States, now Eastern Europeans in larger numbers, etc., etc., etc.
The Angles and the Saxons were but two Germanic invaders out of MANY demographic shifts. |