wrote

I'm not too clear on the details of what youre describing but below the
dpc will always be damp. If youre getting damp up at floor level from
below dpc, your dpc is not sealing somewhere. You can use a liquid
sealant on a concretef loor slab to remedy this.

Thanks NT

The damp is not appearing as visible in the surface of the floor slab at
all.
It is presumably evaporating or tracking up from below (not sure which side
of the dpm) and arriving on the underside of objects placed over cracks in
the floor where the edge of the floor membrane stops.

Maybe I just need to fill the cracks with water-proof sealant?

Phil