Condensation on wall of bedroom solution?

sounds like a condensation problem, positive input ventilation will help cure the condensation your terrace home must be old not to have a damp-course get a local damp proofer to do a survey they are usually free you could also ask the damp surveyor about positive input ventilation if you need further info do not hesitate to ask

As a specialist in Positive Input Ventilation, I agree with Clarke Damp-proofing on each point. If, as it sounds, you have a loft, a unit can be installed in there (subject to the air quality in the loft being tested first). Loft installations are recognised by the Buildings Research Establishment as saving "perhaps 10% of space heating costs". There are a number of PIV units on the market but since they need to run 24 hours per day, efficiency and longevity are paramount. I would also always recommend a high efficiency integral thermostatic heater in any standard domestic situation.

If you have condensation on the walls or windows you need to keep the window open to let some air in and do not dry washing on the radiator.