ondensation induced mould - replaster with an anti mould plaster or replace with green plasterboard?

I would look at your ventilation/extraction........no point in re-plastering in any method if this isn't looked into first. Carl.

I agree, it would suggest you have a problem elsewhere. Once the ventilation is improved (extract fan fitted to external wall would be the cheapest option) just dry out the room properly and maybe cut out the affected section and replace (depending if drylined or wet plastered).