I've included an imgur link to photos I've taken. The mold comes from the lack of ventilation at the skylight. Condensation drops off the window, onto the plasterboard / plaster*.
*In fact, I'm relatively new to the UK --- new enough that I don't 100% know if this is the same as what I know as drywall? However, I'm pretty sure it's more robust than drywall. I think it's a more resilient layer like plaster.
Thoughts on the severity / danger regarding cleaning or disturbing this stuff? We've lived with it for more than a year with no visible symptoms on our parts...
I acknowledge that any advice given on here is not professional / no one can be held accountable for what I choose to ultimately do... The reason I'm looking into this for myself is complicated... I'm just trying to get some answers for myself, and may choose to address the problem myself if I evaluate the risk to be low enough.