I think we have better security in the unremarkable nothing to do with TV office that I work in, you have swipe cards to go through every door, and certain passes can't access certain areas, you can't access where they handle cash for example, or the IT infrastructure rooms, and you have to sign in and be collected by the person you are visiting.
I'm also surprised by the security at NBH, which seems considerably less stringent than at my workplace, which has no connection to the media.
I work in a government building, where the public have access to some areas through one entrance, and staff/visitors through another.
Staff have swipe cards, but only to areas they are permitted to access, and visitors clearly have passes which identify them as such, so should be challenged if wandering about alone.
We have signs on all floors next to the swipe terminals, which warn of people 'tail-gating'. Theoretically, even if you manage to get out of the public area, or 'escape' from the person sponsoring your visit, you couldn't get beyond the staircases or the lifts.