I figured out what was wrong with the story! It’s actually a set of stories, and I needed to go back, cut off a huge hunk of the beginning, and turn it into a story of its very own.
There was still a London Underground. They hadn’t even changed the stops: the Invaders hadn’t dared. Humans had soon learned that the aliens were terrified of fiddling with any kind of engineering that was beyond their capacity to fix, which was most engineering. It was simply easier for the Invaders to put their administrative centers where the old ones had been, even if it did put strains on their security apparatus. That was what the Brotherhood Bureau was for.
But since the Invaders had also grabbed every engineer they could find, kidnap, corrupt, or coerce for their own needs, the Underground was noticeably worse in the places that hadn’t been regularly used by either the aliens, or their gallowglass lackeys. This carriage in particular had been stripped of all of its original features at one point, including the windows. The new government had been hard-pressed to put in even cheap new seats and handholds, and half of the windows were only wooden slats.
Everything was spotlessly clean, though. The Windsor dynasty had views on defacement of public property. And a lot of rubble that still needed clearing up.