So I found this.
https://www.bbc.com/reel/video/p0ftrxhx ... in-england
I'm not sure if they are exaggerating, but they are claiming there is a small bit of the US in Runnymede, where there is a JFK memorial. A gift from the UK to the US. Not far from where King John gave rights to his nobles.
Apparently you do not need your passport to visit it (if you are already in the UK). You might need some form of identification if you drive or take a train there though.
My first thought is, what if relations between the UK and the US deteriorate sharply, and the UK tries to blockade it? Will there have to be a Runnymede airlift, like the one in Berlin? I guess it would have to be by helicopter, because the land is too small for a full airport. Maybe they can land microlights there.
But since no one actually lives there, I guess the Americans could just let it be blockaded for a while. Probably the grass would grow up and be full of weeds, so it would start to look not so nice for a while. But if left long enough, it should revert to whatever the natural landscape for that part of England is.
What if they discover some endangered species living there? Will the US EPA regulate it?
What if they discover there is oil or natural gas under the ground there?
What if some local hooligans start meeting there, and planning terrorist attacks, like smashing windows of people who support rival football teams? Will the UK military invade to prevent the Americans from harbouring terrorists there?
What if you have a single entry visa to the UK? If you enter the UK, then go to this place, and return, are you now an illegal immigrant in the UK?
So many questions . . .