Contrary to what Bede says about the Angles, Saxons and Jutes capturing specific areas of Britain and then working their way West, the actual picture on the ground is likely to have been far more piecemeal, with sporadic settlement not really confined to specific geographic contexts, often alongside rather than replacing British settlements and populations. The idea that certain polities had a definite ethnic identity - the Northumbrians being Anglian, for example - doesn't really appear until Bede's period. It could be the case, of course, that the initial colonies, settlement groups or war warbands which established these polities projected their own personal ethnicities alongside their political power as a means of differentiating themselves from neighbouring or rival polities.

Ethnic identifiers do appear in contemporary Welsh chronicles, where they're typically used to distinguish just which group of English are currently causing problems - the Mercians are typically Anglii and Wessex Saxonum - but the Annales Cambriæ don't refer to there being any real differences worth remarking on. There are also some dialectical differences but nowhere near as much as those which appear in Middle English.