In the period I want to cover with At the Ends of Empire Gildas and St Patrick think of their fellow Britons as Cives (fellow citizens) by the end of it the Britons think of themselves as Cymry (comrades). It is an interesting and much contested period of history.
Following the completion of the Roman Conquest of Britannia the Emperor created local self- government units called civates-plural civitates- for some of the native polities. The historical consensus is that these followed the usual Roman model and were run by an ordo of 100 local aristocrats. The idea being that these would rapidly become urbanised and Romanised (here I’m with Mattingly it means everything and nothing) and thus provide the willing middlemen necessary for the smooth exploitation of the province.
The scholarly view summed up by Sheppard Frere is that the British ordo, in the main, still preferred to live mostly rurally-close to their powerbase. Scholars note that most civitates capitals were by comparison to other provinces a bit shabby -underdeveloped is the term often used.
It has been proposed, partly because of archaeological evidence, that sometime around the Theodosian restoration of Britannia the civitates received permission to bear arms. At this time and indeed before, the towns and cities of Britain were fortified - many in traditional British style. So once again British aristocrats found themselves with in control of fortified sites and armed men.
Things had not come full circle though. Imperial rule had meant huge land appropriations, massive military occupation and consequent infra structure, the establishment of Colonia cities and Imperial estates all reducing the land controlled by the natives.
The fate of the once mighty Brigantes is illustrative, once they had ruled from sea to sea, their civates was utterly dominated by the nearby Colonia of Eboracum (York). The civitates of Britannia were a power- not the power- in the land.
We can say the civitates of Britannia were a political power but there were other more powerful ones notably the Emperor’s administrative nominees and the Army. The ordo of the Colonia and those administering Imperial estates were richer and better connected too.