It's is in the South, near Cambridgeshire, which is about and hour from London. PM me if you want more info.
Well i would guess it is in europe. It just suprises me that All of the people in game speak perfect english. Maybe the Combine mad it the language of the world? No one has accents to prove this though.
I think that human populations have been relocated to compleately different parts of the world. Werther it had any use for the overwatch or was simply done to disorientate people even more I don't know. People who we see in game are pretty much those what one would suspect to see in London or in many locations in US.