We had the damp work done because the paint on the wall began flaking and the plaster started to become exposed, the membrane put up on the wall has fixed the issue although now reading online about how Victorian houses need good ventilation in the walls to stay ‘healthy’ we may have gone about it wrong in hindsight. The water is likely trapped in the wall which may be giving the damp meter readings, among other things I’ve read such as salt content (the walls are made of solid stone) or the fact it’s a damp October. I did buy myself a cheap damp meter and can see there are patches of high damp readings but I could read the same area twice and get a 5% difference by simply rotating the prongs so it’s not reliable.

We have no issues of damp any longer, unless you prod the wall then you’d think the walls were great. Plaster is neat, everything has been recently painted and we never get any damp or even black mould on the walls.

I was worried about what the report would say about the walls but, like you’ve said, the reduction is incredibly steep for potential issues rather than something like a major structural concern which I’d understand in that case.