Due to massive invasions by Franks, Angles, Saxons ( ALL GERMAN TRIBES! ), the ancient Romans, Vikings from several different Scandinavian nations, Normans, and intermarriage with the Celts, Picts, Irish ( not a one of these being Brits! ), as well as Royal and Aristo marriages over the centuries, not to mention those who married Americans of unknown original heritage, you will be hard pressed, if not impossible, to find a 100% pure blooded original Brit in today's England!
What do you consider an original Brit?