Thought you had surplanted us did you, you Anglo-Saxon pig-dogs (Go and boil your bottoms, son of a silly person. I blow my nose on you, so-called Arthur-king, you and your silly English kiniggets. - Monty Python and the Holy Grail)

It seems that the Celts were not driven from southern England as has long been believed.

Analysis of Y-chromosome data by scientists at University College London and reported in the journal Nature finds that "The Celts weren't pushed to the fringes of Scotland and Wales; a lot of them remained in England and central Ireland,"

It seems that rather than fleeing in response to the invasion of the Anglo-Saxons many Celts choose to stay and integrate.