We have a 2-up/2-down terraced house built in 1905 with a restored, but unused, fireplace. We've been living there for five years, and over the last few months have had a couple of small falls of brick spalling from the inside of the chimney (from up near the pot by the sounds of it). The latest bit was about the size of a cigarette pack. It didn't seem damp, although it's been fairly rainy here in London this summer, obviously. I was a little surprised to see that it was brick (with a coating of soot), and not a bit of parging though - are chimneys of this type not parged?
Anyway, there's a vent installed in the breast wall in the bedroom, so it's getting some air (and the fireplace is open). The chimney pot itself looks OK (and is capped off with a vent it looks like, but I've not inspected it properly).
I wonder if there's much that can be done, or is some internal spalling inevitable after a while?