...Arse?Oh please- we British don't need to simplify words' spelling in order to make it look like it's pronounced.
No, you change your pronunciation to Englishify it even when the word is from a foreign source. (Fillet as opposed to fill-ay).
British English > American English.
Written American English is just lazy but I love it when Americans talk .. .. .. .. calling trousers 'pants' and their bottom a 'fanny' *
*yes I'm very childish
For the majority of people, it's going to be American, because that's what foreigners learn. Also, you won't be marked down on British tests if you write in "American" English, especially for the realise/realize thing, where realise is actually the spelling that came after and a lot of British writers prefer to use realize.
Every time I typed that I wrote realise though. >_>
I love you, Adam.