This is the chimney that was leaking. I described it in a previous post, explaining that water was running down through the attic and dripping from the ceiling in our parlour. We do not use this fireplace, because the chimney was so dodgy. It was clear that water had been leaking for quite a while. We decided that we should avoid using the fireplace when we bought the LBH in July.
We plan to remove the chimney completely and patch the roof accordingly, perhaps next summer. We would like to put an efficient heater in this room, one that fits with the Victorian decor. For now, however, we decided that we had to deal with the leak in our roof.