Seems solid logic to think it's in the UK, but no evidence really to indicate that it's Zero and not Big Boss or Solid Snake.
This all seems fishy to me though, since so far the whole riddle has been way too easy to crack for people. Within an hour of that trailer being released, people had already gone oh that's Volgin, oh that title says MGSV, oh that's Big Boss 'cuz scar. If it really ends up that the prevailing theories are true, I'll be disappointed in Kojima. This was the man who made the world think that MGS2 starred Solid Snake!
It's easy because of how connected everyone is now. If there are any clues at all there are enough people working together that they'll figure it out in no time no matter how difficult Kojima intended it to be.
It's easy to say it's easy because you read a rundown of what everyone else had already figured out but you probably wouldn't have noticed a majority of the connections if you had watched the trailer than turned off the internet.
The first time I watched the trailer, I thought to myself: Oh, this looks like that OGRE engine or whatever. Oh, that dude looks like Volgin. Oh, that guy looks like Snake. Oh, Moby Dick's logo is way too terrible for a new big studio. Oh, Kojima is at this event for some reason. The more obscure things that surfaced later were just the cherry on top.
I agree though that if a riddle is solvable, it will be solved on the internet. The difference is, when I heard about what people found in Fez, my jaw hit the floor. With this, I was just confused why they tried. There's still plenty of mystery around the trailer, but the whole totally-not-MGS veneer is kind of boringly thin to the point where it's kind of a wonder why they attempted it.