Sure, accents are partly markers of social status, but it's quite wrong to ascribe the diversity of accents in Britain to this. There was never a period where everyone in Britain spoke with the same accent.

> but it's quite wrong to ascribe the diversity of accents in Britain to this.

No one, AFAICT, did that. The reference to “modern British English” is not, as I read it, a reference to “the current diversity of British accents”, but rather “the current dominant British accent”.

The current dominant British accent, if there is such a thing, isn't a marker of social status. If you're referring to RP, then hardly anyone even speaks RP nowadays (even the Queen only makes a half-assed effort...)

I would say accents in the UK are a combination of social status and location.

They're a combination of that pretty much everywhere, but it's not clear to me what the "dominant" British accent is supposed to be. If there is such a thing, it's probably some kind of fairly unremarkable Estuary accent that doesn't have any strong connotations of a particular social status.

"They're a combination of that pretty much everywhere"

Fair point - I would also agree that the idea of a "dominant" British accent seems a bit odd - certainly not in terms of what people actually sound like (rather than the broadcast media).