Ok let's recap; the British dialect, I.e British English, is a sort of umbrella term which encapsulates of a wide of varieties OF British English- Scouse, Welsh, etc- which also acts as a Standard level of English, a basic framework of English English. British English is a thing. Read a few papers by Peter Trudgill or read his book "Accents of English" if you care that much.

I'll accept that however it doesn't change the fact that it was accents that were being discussed and not dialects(until you brought them up) Even if it were for arguments sake, an umbrella term for a group of dialects is somewhat different from a specific dialect is it not? I wouldn't of thought it needed explained but the original comment was directed at the fact that americans are under the very naive opinion that anyone from Britain has the same accent. You know the one, it's in just about any film/tv show/cartoon ever created by americans that features any character from Britain. The reality is that nobody speaks like that (admittedly nobody may be an exaggeration as it had to come from somewhere) there fore this mythical "british" accent does not exist.

I was marking a paper on spectograms and acoustic phonetics earlier so you can forgive for not going into detail. Please read a book, I cba.