One of the Sharpe’s Rifles sequels had a Virginia Tory who inexplicably spoke like Elvis.
There was a BBC cop show in the 80s, “Dempsey & Makepeace,” about a “street tough” New York cop paired with a “tough but sexy” female London detective. Michael Brandon, who played Dempsey, complained in an interview that Brit directors only wanted him to talk like “a cowboy from Oklahoma.”
TV is not, and never has been, a good place for accent authenticity.