For some reason it’s easy for British actors/actresses to do a believable Southern accent.
Got a sales call one day from a very British lady. After talking to her for a minute she asked me “From what part of England are you?”
I was kinda confused. Just said “pardon me?”
“I would guess Northern England. Wales?”
Me: “No ma’m. Born and bred Central Alabama redneck.”
Her: “Oh dear!!”. I’m not sure exactly what she meant by that......
They do have a knack for that.
Not sure if you ever watched the tv series "Fringe," but Anna Torv, one of the main stars is Australian. I never would have known had I not done a search for her on IMDb.
This is because the classic Southern accent is the descendant of the Scots-Irish accent of the original Scots-Irish settlers of the South. This makes it pretty easy for a British speaker to emulate the Southern accent but it's a little harder for them to consistently pull off the more homogenized 'American' accent that you hear from most newscasters. One of the ladies in our house is an actual Lady and her family is from near London and this is what she told me.