Getting a woodburner installed tomorrow, so have moved all the furniture out of the room and can see the extent of the damp around our chimney. Any ideas?! It's been growing over the last two years (when we moved in). We haven't used the fire in that time (it was used by previous owner). The wall is the party wall with next door. They just have an electric fire on their side, and no radiators or other sources of water I can see. We have a radiator on the wall to the right. There are a couple of other small patches on either side of the chimney breast also that you can't see here. None further up or up the chimney breast.
Hoping that using a fire will help dry it up. But any ideas what it could be? Thanks in advance!