The cavity below was absolutely stacked to the joists/floorboards with rubble and debris. This had breached the damp proof course and all he moisture leached from outside in...
The walls are a little bit damp but hoping that this will clear up the issue!
Same thing with us - rubble had filled the gap between the dwarf wall and external wall, breached the DPC, and the joist were pressed against external brickwork.
And there were literally tonnes of rubble under the floor too.
Did you find out what caused it? Good jerb fixing it.