benpost wrote:
where i only own the ground floor...

so cavity wall insulation isn't really an option as upstairs dont seem
to have the problem as bad.

a plasterer suggested insulating plasterboard on top of the walls
which takes about an inch of room space? but then there are
radiators, wall sockets, heating pipes etc to think about?

are there any other options to try and stop this cold wall attracting
the water vapour and turning to mould? i have heard of anti mould
paint or wallpaper but i'm guessing these aren't a real solution?

A very thin layer of insulant - like polystyrene sheet or cork tiles -
will generally be enough to lift the surface temperature above the dew
point and stop condensation.

But an inch of celotex is a lot better, and yes, it does mean moving
EVERYTHING attached to that wall.