hi there
ollie, if the walls are plasterboard,
then you would be looking at removing all the affected areas, the spores are able to live in the plasterboard.
microsan will have an effect, but you cannot guarantee it.
you need to lok at a professioanl strip out, moisture level monitoring, and possibly a drying regime required.
if you would like to talk about this please call me in the morning 07771 526246.
where abouts in the country is this property.
regards
martin