If this fails I have got myself into trouble! I spoke with the painter about the damp problem. And he suggested he line the wall with aluminium foil! It sure stops any moisture coming through. And then he'd line that with the thermal insulation stuff, to sort any condensation issue. That was a tip from my neighbour who has a similar wall. And then lining paper over that. And then paint that! A big job. But it fights damp on two fronts so it’s worth it.
When he had done the foil the room looked really weird. And I think that if I ever regret this, and want to get rid of it, I will have to get all the plaster off the wall. That would be quite the job! But let's hope that never happens. And when it is all done I can start putting furniture in the room and use it!