Well there's the Romans, the Saxons, the Angles, the Danes, the Norweigians, the Frisians, the Greeks , the Phoenicians (they all came for tin and other metals) etc etc etc..... we'll take the lot lol. the Celts are natives though...we think.
We do quite happily absorb people from other countries but we don't then kick them out, they just all become English. That's where he had the history wrong, we don't absorb them, interbreed then rise up and kick them out, it didn't happen like that. They get subsumed into our way of life and culture even the Normans did because then we went on to have several wars against the French!