Google personalizes results quite extensively these days, largely based on your location. Google believes based on that, and probably your previous searching and browsing habits, that those .co.uk sites are more relevant to your interests. After all, this is the company that has patented and is developing the idea of "Parameterless Searches", where they assume what you want to know before you even ask... (more info http://www.seobythesea.com/2013/07/google-parameterless-sear...)

Are your google account settings localized to the UK? This issue used to regularly drive me crazy.

Fortunately they now have a worldwide setting. At one point you could select only 5 (or was it 7?) languages for which Google would show you results. They fortunately fixed that.

I mean, who would want to search _all_ the internet?