If it does start to reappear then I would suggest you get someone in from the council to figure out exactly what it is. If the room is well ventilated, and you use a dehumidifier, then there shouldn't be an issue with mould so it could be something different.
Providing it is mould, I would imagine that killing the spores with the bleach solution will be enough to remedy the issue - just make sure you rinse the walls after using it before applying your new paint.
I would suggest using an anti-mould paint such as Dulux Trade Mouldshield but that is pretty expensive (especially if it doesn't work!) so you might want to opt for a regular eggshell finish emulsion, which should be good for cleaning any further mould spores from.
As for using sugar soap to clean it, I don't think it would be the best product because it can be harsh on some paint finishes and is usually used to prepare surfaces, or for cleaning heavily soiled areas.
I hope you get it sorted.
Providing it is mould, I would imagine that killing the spores with the bleach solution will be enough to remedy the issue - just make sure you rinse the walls after using it before applying your new paint.
I would suggest using an anti-mould paint such as Dulux Trade Mouldshield but that is pretty expensive (especially if it doesn't work!) so you might want to opt for a regular eggshell finish emulsion, which should be good for cleaning any further mould spores from.
As for using sugar soap to clean it, I don't think it would be the best product because it can be harsh on some paint finishes and is usually used to prepare surfaces, or for cleaning heavily soiled areas.
I hope you get it sorted.