So - we are now very sure it's coming in from the crack in the chimney crown. It's actually audible in the chimney breast in our bedroom when it rains.
Except.... the insurance assessor who came out said it wasn't. Definitely not the crack in the render (you know the one @PigletJohn thought looked as if it had been put on with a fork by a man with no thumbs?) no no, definitely not that, it's nothing to do with the chimney at all, he says, with his camera on a stick. The roof is sound, the flashing is sound, there's nothing structural at all the problem. It's coming in round your bathroom window he says.
Despite the bathroom window not being where either the noise or the discolouration is, or despite one of the five builders who's looked at it already having sealed it, but hey ho, definitely not that. So - no claim, because the bathroom window is wear and tear, and the chimney - which would have been covered, due to having been recently refurbished - isn't the problem.
Got someone coming out for a look next week - this is the earliest we can get anyone.
Last night part of the bloody ceiling collapsed in the dining room in a shower of cob wall, and water's now dripping onto my dining room light fitting. Turns out the non issue has escalated quite significantly. It's a very small piece of plasterboard but am I being unreasonable to go back to my insurers and tell them not only was their assessment wrong, but their reluctance to act has actually caused more damage to my house?
(I'm working on the assumption that they would have had access to someone a damn sight quicker than I do, since I've been trying to get someone out for almost a month!)