Some SEO experts have commented recently on a new quirk of google that has led to interesting results. When you type in words like 'colour' and 'search engine optimisation' into Google UK, the first SERP page is showing results from american spellings of the word, for example, if you type in 'colour' the first result is the wikipaedia page for 'color' (american spelling) and other search phrases which are obviously international english spellings are also showing american spellings for the top results.

With google trying to push their localisation (sorry should that be localization?) services and personlised search, it seems odd that the american pages are showing for uk phrases.

I'm sure this quirk will be addressed soon, but in the meantime, you need to put more thought into copywriting articles so that you use a consistent style of language. This is not only better for search engines, but for your website visitors too.