Black mould on walls

I have a downstairs loo and utility room that is built out of housebrick only. Last year, I painted the brickwork inside. Now I have black mould covering the walls and ceilings. Is there any way of stopping the mould from spreading? The rooms are not heated so get very cold in the winter. I find if I heat the rooms, a huge amount of condensation appears on the walls. Heated or not, though, the black mould seems to be getting worse. Is there anything I can do?
Thanks for reading this.

I'm very sorry for missing your post, do you still need help with your problem.