Oh yeah if we’re doing an AU I’m down for that, I was just talking about the actual construction of them.
Still my personal preference would be the actual Metro, especially since there Are parts of it that have remained unexplored in the current media available and are ripe for some interesting work.

But yeah London’s metro gives us a lot to work with.
I suppose we could fill in the local wildlife by saying some creatures evolved from animals that were in Zoos?
To give us a bit more in terms of variety and working space.

Also we could have Britain’s stance in the Cold War to be far more allied with America?
Basically making it a two v one scenario, meaning that there would be far more in the way of military installations and funding to aid with having a larger pool of weapons and ammunition to go around.
As well as that Britain would have acted as a forward base for the US allowing for a larger variety of arms.