Try: www.google.co.uk/?gl=GB
That should give you the same google as if you were in the UK. Or, that is what I use if I want to have the "pages from the UK" option.
Why do I have to tell each website the language I want in a website-specific way when there's been a standard HTTP header[1] to do exactly that for more than 20 years?
I'm honestly asking: do web developers ignore know basic HTTP features or is there some specific reason?
I don't know what Google does exactly, but at least in my case the header works as expected. I live in Germany, have set the language to en-US everywhere and Google serves me an english page just like I want it. And I'm not even logged in to Google.
I agree that it should not be like this. I only offered a workaround, but in this case it's not only the language that changes, the entire site is served as if you geolocation is GB.