Ian
Not too sure how to attack the problem, I would start buy using a amoniated fabric spray, but make sure you vac it well first as applying water to mould just makes it worse, alot of it will come off without damage with a good vac.
Had a problem with a sofa once on a farm, cleaned it and got a call saying it was covered with mould a couple of days later, so went had a look, cleaned it again nearly dry when I left, phoned the next day all was good, a couple of day later a call again "mould" No it was not mould we figured out it was FLY S***
James