I asked my editor to use US, rather than UK, spelling. I'm sure I'll get hassled about it but I had to choose one and one of wee books on publishing said I should use US spelling.
So there will be more zeds in the book than expected.
But - or should I say butt? - since the book is set in the UK (in a fictional Scottish city called Watt's Bridge) I needed to stick with UK dialogue. So we've stuck with ARSE rather than ASS. I tried to write around it - ie choose a different word - but, really, if you gonna call someone an ARSEHOLE (or even an ASSHOLE) or say that something is HALF-ARSED then there just aren't any appropriate synonyms.