Who searches ‘Pages from the UK’?
Google.co.uk users get an option Google.com users don’t when searching. That is to restrict their search query to ‘Pages from the UK’.
I never use it myself, but I came across a Hitwise article that mentions that 14% of UK Google searches have the option selected. So, if you operate in the UK and your site doesn’t appear under a ‘Pages from the UK’ query, you could be missing out.