BTW Any self-respecting British ghost hangs out in a castle. Not a pillbox.
As a British kid who would play around such things the vibe is crack-den / toilet. Expect graffiti, ancient garbage, drug remnants, poop. The ones in the link are like the stately homes of pillboxes!
The vibe is small, dark, damp and with a strong smell of urine. Each to their own!