Thank you for the prompt reply...Its mould caused by condensation.
There are a number of things you can do:
Stop drying clothes inside (if you do)
Keep bathroom doors closed and windows open when showering and bathing
Ensure your kitchen has extraction
Ensure adequate ventilation
Use anti mould paint
Consider a polystyrene wallpaper in affected areas
Insulate your walls (expensive)
I have been getting quotes for cavity wall insulation
From personal experience, the single biggest thing you can do is to stop drying washing indoors (if you do).
Convinced the better half to not do it apart from in a well ventilated room, and its made a huge difference
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