Just to clarify having read through the above.
The celotex bonded to ply is for placing on top of joists to for a warm roof with a roof finish on top which does not need ventilation. You cannot simply stick the ‘celotex’ to the underside of the ply you have installed already.
All insulations that have a a rigid sarking board over need to have 50mm void ventilated at eaves and ridge, otherwise you are asking for trouble with condensation which in this case warm moist air has travelled up the void, got cold, condensed and is now running down the roof.
Usually celotex joints in boards are butted tight together and sealed with a foil tape to create a vapour control layer. You have nothing at present stopping moist air reaching the cold side of the insulation.
Unfortunately looking at the photos you appear to have purlins up against the underside of the ply that would stop being able to effectively vent void.
Otherwise in simple terms you could have had a continuous nominal 10mm gap top and bottom – with a bit of insect mesh to stop critters getting in and making your cave their own.
Without going into condensation / classification or useage there is insufficient source in the building to create that amount of “condensation”
Unless of course the OP was working in there with the door closed – humans, especially when working physically, create a fair bit of moisture.
All my comments are based on what would need to be done on a home, but it’s little consolation if stuff in the cave gets knackered.