Carolyn wrote:
I had a surveyor round the house as part of my Remortgage process. He used his sensor ...
What I want to know is; how foolproof are these readings?

About as much use as waving a crystal and chanting an incantation.

His gizmo was of the type that had a series of lights climbing up
from green, then amber, to red, in a black box affair, with two metal
prongs he put against the walls.

Hm, did he make it himself from a traffic light simulator circuit and
some parts from Maplins,

Also, what sort of cost am I looking at to get this addressed? I know that it will
probably mean all the plaster knocking off to about 2 feet up from the skirting level,
then replacing once its dried out, and finally repainting it all

Which, if you did have damp, would just mean the damp would come back a
few months later.

If you've lived in the house for a while you should know if you've got
damp or not. If it doesn't smell damp and you aren't getting
mould/mildew/rot then it probably isn't damp, and Mr Surveyor won't be
getting his thank-you bottle of whisky from whichever damp proofing
company he professionally and impartially suggests.

If you do have damp then it will be -

- rising damp, which some people say doesn't exist
- penetrating damp, which usually means raised soil/paving levels
bridging the damp proof course, or water splashing above the DPC
- condensation, which means open the windows, extractor fans in the
kitchen/bathroom, and heat the place.

Owain