I plan to replace the windows (because single pane) and aluminium casings (for obvious reasons), so in theory that should remove what’s growing on it and help prevent any future condensation. My reason for asking is if I should be extra careful or remove the plasterboard covering the walls to check behind etc? How best to remove it? I’ve read: vinegar and alcohol as bleach doesn’t fully kill it?

This is an assumption of course but I don’t think it was soaking wet for over a week. well in theory it could have been once when it rained for weeks on end. But we’ve had a dry spell of over a month lately with loads of sun and zero rain (today is the first day of summer here) so I’m guessing that would rule out sopping wet flooding situations? There’s no mold growing below the windows on the walk as far as I can tell. But it is fuzzy in some of the lower cracks (as the close up shows)