As I've been saying for a long time now, Cavity Insulation is inappropriate when applied in a retrofit situation. If it wasn't there to start with, DON'T put it in. This also applies to internal and external insulation.
BBC report on cavity wall insulation failure
If you even SUSPECT failure - and have any of the symptoms of this - mould growth on walls, dampness appearing where none was previously, asthma suddenly developing - don't hesistate to contact the installer - or failing that (most don't want to know) - CIGA - the cavity insulation guarantee authority (they dont really want to know either) - and failing that, tell us and we will do a full survey, and advise best course of action.
This also applies to anyone thinking of using internal or external wall insulation. There is simply NOT enough research into what happens as houses are insulated. Government claims about heat loss through solid walls are wrong to start with, and the scientific basis for energy savings through insulation are flawed. If you are even considering insulation, speak to us first, or do your research - it is more likely you will benefit through simple things like shutters on windows, thicker curtains, changes to heating systems, reducing humidity internally.
Pete