Picts, Celts and Britons inhabited this Isle long before the Angles, Saxons and Jutes rocked up.
They were pushed back to the coasts and the highlands of the nation...which is why Cornish are in a corner of the land, the Scots are scattered across the higher reaches and the Welsh are shoved into a principality. The Angles, Saxons, Jutes and Vikings ravaged most of the central lands and settled in Wessex, Kent, Yorkshire, Lincolnshire and Sussex.
At least in Northumbria we have retained some of our Celtic heritage - alongside the notable Viking influences.