Recent studies considering modern and ancient DNA show that about 25-40% of British ancestry is Anglo-Saxon, with a high in East Anglia and gradual decreasing as you move north and west. While the Britons of Roman times look like the Welsh.
Winston Churchill wrote about this, in The Birth of Britain, the first installment of his history of the English-speaking peoples. He mentions that place names in Sussex suggested total replacement, while the West Saxon legal code made provision for the rights of Welshmen.. But he didn’t know how much replacement had occurred. Still, he said “.. we may cherish the hope that somewhere a maiden’s cry for pity, the appear of beauty in distress, the lustful needs of an invading force,would create some bond between victor and vanquished. Thus the blood would be preserved, thus the rigours of subjugation would fade as generations passed away. The complete obliteration of an entire race is repulsive to the human mind. There should at least have been, in default of pity, a hearing for practical advantage or the natural temptations of sex.”
However, being repulsive doesn’t stop something from happening. This time, it didn’t. Perhaps Churchill’s ghost, or his ghost’s ghost, is pleased by this result.