The wall is internal on both sides. There is no evidence of damp anywhere else. The plaster has bulged. Most grateful for any pointers as what the problem could be ??

Simon, March 2008

well damp does not mind which wall it attacks you will get damp on inside and outside wall,anywere the damp course is broken or bridged
you do not say if floor in floor boards or concrete if floor boards lift and check pipework.also check no rubble and soil is piled up against the problem wall under floor as this will cause damp to rise,if concrete check around pipework and see if wet patch if so this would point to pipework leaking
also there is an argument that the radiator would make damp look worse as it drys the wall behind on pulls the dampness out

tony, March 2008