I tried .ca rather than .com with a London based query. It gave me 3 Canadian sites at the top and then the usual UK sites from positions 1 to 7 in much the same order. (For the geographically challenged there is also a London in Ontario)
.com gives me all UK sites on the same search.
If I repeat the query substituting Essex (there are, I think, three towns with that name in New England) the first page is the same in .com and .uk with purely UK results
Repeat search for a non uk location and I get the same non uk results.