Being English ( or rather half English half Welsh), I use English as I know it, with the spellings of words as used in the UK, (eg: colour, centre, traveller, pretence, manoeuvre). Fortunately of course, there is rarely much more than one letter difference in the spellings of words in English English and American English, so the understanding is clear even if people from across the pond may think the word is spelled wrong.
Although I don't use American spellings, I do sometimes use words which are more common in American usage than British, because of course the majority of readers are likely to be American, and I want to be sure my articles are understood. So for instance I often will refer to trucks, candy and gas (all of which are fully understood in Britain) though in my country we would more commonly use the terms lorries, sweets and petrol respectively.
I would draw the line at using American words which are largely unknown in Britain.