@An Sionnach Seang - I hope it's not too late to make this request. Could you have Russ work up to more "posh" British accents - "Southern" or "BBC announcer" type - as he seems to be learning his lesson. Then, when it's obvious that he's showing the reader why he's wrong and choosing to remain so,* have him slip back in less "refined" accents. Sort of like
Flowers For Algernon, where the narrator gains intelligence through a science experiment, only to lose it and return to his exceptional self.** If you feel you're already past the point in the story arc where you can work it in smoothly, no problem. I just wish I'd thought of it earlier.
*Still one of the weirdest narrative devices I've ever seen in an autobiography, even for a habitual liar.
**No offense to anyone in the North or Midlands of England - "some of my best friends are..." etc. (true, actually) I just imagine Michael Palin doing that accent, and it cracks me up.