Just registered because of the problem below!
We have the ground floor of a 1900 bay fronted Victorian terrace. We have water running down the wall of the room which used to be the original back room (all these terraces are standard - one room at the front, one just behind it, then an extension going back not quite as wide as the front so that two neighbours share a wall but there's a gap between the next two).
The damp wall is internal, shared with next door. We have a further (new) extension past this into the garden but next door does not. There should not be any water pipes on this internal wall as traditionally they run on the other side of the houses. The flat above us definitely has their water on the other wall and I think next door still has an outside toilet and a bath in his kitchen!
The damage to the wall seems too much to be just caused by condensation (in my opinion but I know very little!). There is a patch of blown plaster and other patches of plaster are rough, not bubbled and soft, but little hard lumps under the paint. The metal strip which runs down the edge of a shallow alcove under the plaster has rusted and is loose, suggesting the plaster under it has crumbled. The water is running in drips on the surface of the wall and the carpet is wet at the bottom. The whole wall seems affected, top to bottom.
Could all this just be caused by condensation? Or should I be calling someone out to look for a major problem? No other walls in that room seem particularly damp, even though they are the same original brick. The extension which goes back further is bone dry and the wet wall is right in the centre of the ground floor!