As far as I know depending on where you are searching from google shows different results. So for example:
I run a search from the UK with Google.co.uk and my keyword comes up in position 4
I run the same search from the UK with Google.com and my keyword now appears in position 13
Obviously Google takes a lot into consideration when showing rankings but two things that come into play are your location running the search and the location of the server that hosts your site.
The best way to get the most accurate result is to run a search in Google as if you are in the country that you want the result for. So if you want to know the position of your keyword in Google.co.uk as if you are based in the UK do this.
There is a plugin for Google Chrome which allows you to select a country from a list and get back results as if you where in that country running the search:
http://www.redflymarketing.com/internet-marketing-tools/google-global/
Hope this helps