There is also a Zinsser equivalent which I think you prime and then topcoat with a different paint.
I just grabbed the Roseal as that was available in Screwfix at the time. Which you can't paint over. I'd recommend following the instructions properly for the best chance of success.
Not much of a post but we haven't yet had any mold on our bathroom ceiling since painting with Ronseal antimold paint.
Quite pleased as it was a bit of a last min slapdash job in the gap between jobs and whilst looking after child no2.
Now very tempted in the spring to go around and do a proper job in all the window recesses.