It's actually rented and initially pre-dates the tenancy. House is up for sale so they wanted to get an idea of how bad it was/how much it might cost to determine if the landlord would sort it whilst in-situ - which doesn't seem likely now, christ!!
To be fair there is zero ventilation in that room as the windows are painted shut, and all the woodwork is over 120 years old. There's no signs of rot on the outside of the frames.
To add also, there's a tonne of red dust/particles on the floor below the skirting, along some of the painted skirting areas as well as inside the cupboard which can be seen in one of the pictures.
I shone a torch on the bigger cracks in the timber inside the cupboard and there was quite a bit of white 'webby' film on the exposed (/non painted) timber.
Wanted to get an idea from experts/people who have dealt with what I presume is dry rot in a friend's house. Posted pictures, one from August and a comparison to now where it seems to have gotten significantly worse.
It's downstairs, there's no immediate current source of moisture outside...