RIGHT!
Here is his logic which backed mine up!
When it rains the walls down below do get damp - I haven't installed the dimpled membrane and drainage channel around the perimeter yet.
So water is effectively in there.
Evaporates and hits the ceiling but also the plastic sheet over the walk on sky lights ( plastic sheet is wet on the inside! ).
Drips back to floor or tracks along any deviations in the concrete ceiling.
As water is never actually removed (until drain, MVHR etc. are in) the cycle just repeats
I've got the actual roofer guy coming to look tomorrow so I hope his logic backs this up!