To me, the Dark Ages are dark for a fairly specific reason.  We know that in 410 Roman Britain got rid of the imperial officials, and that by the end of the 'dark' period there had been major changes, especially huge linguistic ones, with Germanic and Goidelic apparently at some point replacing British and Latin over very large areas.  What is especially 'dark' about the intervening period is the extraordinary racist codswallop that has been thrown in to cover the lack of documentation – codswallop that would seem to defy most of what can be known from archaeology and genetics.  Somehow the Romano-British got themselves replaced by some other people called 'Celts' who (they obviously had good chauffeurs) spent their time being 'driven' to all sorts of places, all the three to four millions of them, by what looks likely to have been a few thousand Germans.  I doubt , and I do not believe Bede's sources were up to much, or that Gildas was any sort of a historian.

'England' didn't exist, of course, and a normal proportion of the British were Roman citizens for a very long time, the Province/provinces being perculiarly prosperous in the third century.  When they ceased to be useful to the British Romans, the imperial officials were hoofed out in 410, and Britania Prima, in particular, got on very well for several generations thereafter.

I used "England" for simplicity because that's what we call it now and because I don't like typing "Britannia." 🙂

Well, I never use it thus, because I come from Britannia, not England, a country that does not wholly enthuse me.  'England' is the flat bit on the right. 🙂

The only 2 things that ever came out of England that were any good were 1.) America and 2.) Led Zeppelin 🙂

I couldn't possibly comment! 😉

and no electricity yet (or is it the arrows?)