It's true that "cigaret" is only used in US English. But even there, "cigarette" seems more common to me, and the other spelling strikes me as old-fashioned. So I would stick to the word "cigarette" wherever you are -- nasty things though they are -- and you'll be correct.

Edit: They're pronounced the same way so it doesn't matter which one you'll use if you're talking to some one but if you will write it and you want to be specific then Cigarettes is British while Cigaret is American. (Fag is slang for British cigarette) http://www.collinsdictionary.com/dictionary/english/cigarette