Scott - British Male
Scotty always referred to himself as being Scottish, never British, or as being from the UK.
It pretty safe to say that he is not "British."
Hoshi Sato's speaking voice is the same as Linda Parks, she wasn't employing a accent. What we were hearing on the show was Linda Park's normally accented speaking voice. A accent she came by through growing up in San Jose, California
Hoshi Sato possessed an Pacific coast American accent, and most likely was a "American Female."
Uhura is supposed to be from Africa, yet speaks with an American accent.
Scotty can still be British, even if he never mentions the UK. Did McCoy ever mention the USA?