Plant some button mushroom spores, at least you get some free food then... How old is the property, solid wall? I had similar problems, as said ventilation is key, I've installed two extractors running on humidity stats, one for bathroom, one for kitchen, started digging out the front garden as its filled with soil (over a foot from ground level) causing water retention and not allowing the walls to breath much. Once that's done, I'll add an additional down pipe (no down pipe currently) as well and maybe a third extractor to an additional room, but there has been huge improvements with every improvement done, joys of Victorian build!
Check for external wall for moss growth, moss helps hold moisture in, dettol kills moss quite well from experience, which I was suggested by a civil engineer friend, with black dots, I know chemicals containing copper they hate, otherwise top tip is usually use a bleach/chlorine solution to clean the area, but still try and fix the original problem otherwise you will get the mould returning. I know on fresh plaster its very rare to see mould due to the high levels of alkaline from the lime, which mould absolutely hates.
