Just been reading this thread from the first post and was thinking exact same thing - read the book a few months back. Then I got to your post - so you beat me to it
There were a couple of armed police patrolling Churchill Square a couple of weeks ago.
I think it's just a sign of the times unfortunately.
Personally find it quite reassuring though I do have an initial reaction of "Whoah, that's a big gun" followed by a little "Ah yeah we do live in a world where lunatics can kick off at any time" thought.