S/z

[irmamar]

There are words that can be written in a different way in British and American English, above all these words with s/z, I mean, words like: analyse/analyze, realise/realize, etc. I know that those words written with "s" are British, although I know that they can be written wit "z" in British English as well.

I'd like to know if British English people prefer to write those words with "s" or with "z" and, if they preferred "s", would they/you distinguish if a text is written by an American or not when you're reading a text with "z" (if there aren't another words like colour/color, etc., of course, which could give you a clue)?

Another question: if I had to write several words like those in a text, would it be important (gramatically) if I wrote some with "z" and some with "s"?

These questions could look like stupid ones, but I'm very interested in your answers. Thanks.