The received wisdom seems to be that imperial officers in the original Star Wars trilogy all have plummy British accents. And it's true that most of the top guys do: Tarkin, Ozzel, Piett, Veers, Jerjerrod, Tagge. But I can think of at least ten who don't:
"Holding her is dangerous!"
"An escape pod was jettisoned during the fighting, but no life forms were aboard."
"Don't try to frighten us with your sorcerer's words, Lord Vader." (Motti)
"Our scout ships have reached Dantooine. They found the remains of a Rebel base." (Cass)
"Captain Needa, the ship no longer appears on our scopes!"
"Command station, this is ST 321. Code Clearance Blue. We're starting our approach. Deactivate the security shield."
"Inform the commander that Lord Vader's shuttle has arrived."
(Interestingly, this is a British actor whose line is dubbed by an American.)
"Shuttle Tyderium, transmit the code for shield passage."
"You rebel scum!"
Does anybody know if the total number of clear-cut British-accented officers exceeds the American tally? In addition to the six mentioned earlier, Captain Needa clearly has a British accent, so that's seven to start with.