Here's a great list of common interjections which you might find useful - http://www.dailywritingtips.com/100-mostly-small-but-expressive-interjections/ British and American interjections are mostly the same with a few differences. "Gosh" for example is quite an English word, as is "bravo".

"gosh" is not just English! Americans say it all the time! Expressions vary depending on what part of America or Britian you are in. "Bloody" is one that usually is only Brit but in some small parts of US it is also said. "This bloody car won't start." some i dont hear in US: "taa" can meaning "thanks" "cor" or "blimey" or "cor blimey" "hell's bells" one's that are the same US and Brit say "your pulling my leg" to mean " your kidding,right?"Brits take it a step further and say "go ahead pull the other one" "jesus on a bicycle or christ on a bike" sort of means "this is incredible" "gee, gosh, golly" "jimeny crickets" is something i dont hear in brit they are what people say instead of "o my God" because people disapproved of using God in this way. Most importantly I cant think of any that are not mutually underdstood