google problem - 'pages from the uk only'

[Timbow]

I have been checking a site for position in google. I am in the uk, the site is hosted by a uk company with uk servers, the subject matter is uk and I am using google.co.uk. I put in my search terms and I find my site at around 30th place. Then under the google search box I click on Search Tools and change from The Web to Pages From the UK . The results are almost the same but my site has disappeared.

What is going on here? How does google determine the location of a site? Why should it think my site is not in the uk? How do I fix this?