This is true, but you could also say the same about the phrases "English accent" and "Scottish accent" -- a Scouse accent sounds nothing like RP, and a Highland lilt is very different from the accent in the Gorbals.

And the Appalachian accents of Justified sound very different to the Mid-Atlantic accent of Frasier Crane -- yet to me, as an outsider, there is still an indefinable "Americanness" common to them all.

People who don't live there, or are selling to people who don't live there?

In the UK we use the phrase "American accent" and it's OK. It means "there exists an American who would use this accent" not "all Americans use this accent".

There's plenty of difference within English accents as well. I'll generally classify any of them as English, I think.

That said, when I use the term British accent, I do usually mean English, I think. Sorry. Also sorry for all the times I used England when I meant UK, or UK when I meant Great Britain, or vice versa.

Pretty much everyone except British people uses this term.

The reality is that no accent (not even english ones) sound like each other technically. Consider a south east accent with a scouse accent, for example. Both English, both nothing like each other.

I believe the correct expression would be "British accents".