Generally we refer to the English spoken in the British Isles as "British English," but the distinction could be made between various forms of it: Irish English, Scottish English and English English.
Because people speaking in any two separated regions will eventually pick up their own quirks of speech which do not transfer between two regions because of the separation.
Yes, very much so. Australians have a unique accent and idiom, and spelling intermediate between UK & US English (with US spelling becoming more common).
no you also get South African English and probably a few more, like Australian or New Zealand EnglishEnglish is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread...