One of the features I've remembered (having imbibed Rosemary Sutcliffe at a tender age) was her consistent use as characters of what she called "the little dark people" - NOT the Celts, but rather, the people preceding the Celts, who she symbolized in various ways, including:

a) A matriarchal society, based on worshipping "The Earth Mother" rather than the patriarchal society of the Celts and their worship of the sun (one of my favorites, here, is "Warrior Scarlet," her one foray that I know of into iron-age Britain);

b) Conquered by the Celtic tribes, they had withdrawn to the hills and small farming settlements, frequently dug-down below the level of the main village (you'd descend to enter a turf-topped bothie);

c) More prevalent in force in Wales, Cornwall, and the North of England/Southern Scotland, but always in small communities, without major political organization.

d) Viewed as suspicious by the Celts and as irrelevant by the Romans.

You know, I have NO idea what Sutcliffe was discussing here, although I could talk more about the portraits she paints. So just who ARE these indigenous Britons?