It is also admitted that there exists a large mixed population of Celts and Teutons in Strathclyde and Cumbria, in Lancashire, in the Severn Valley, in Devon, Somerset, and Dorset.

The northern and western half of Britain is acknowledged to be mainly Celtic.

Thus the question really narrows itself down to the ethnical peculiarities of the south and east.
Here, the surest evidence is that of anthropology.

We know that the pure Anglo-Saxons were a round-skulled, fair-haired, light-eyed, blonde-complexioned race; and we know that wherever (if anywhere) we find unmixed Germanic races at the present day, High Dutch, Low Dutch, or Scandinavian, we always meet with some of these same personal peculiarities in almost every individual of the community.

But we also know that the Celts, originally themselves a similar blonde Aryan race, mixed largely in Britain with one or more long-skulled dark-haired, black-eyed, and brown-complexioned races, generally identified with the Basques or Euskarians, and with the Ligurians.