'To declare the surface "damp" requires a physical inspection of the surface'
That's worth knowing. There could be a difference between the ATC and duty officer's version of 'damp' and that of the operators.
From the AIP:
'DAMP — the surface shows a change of colour due to moisture.
Note: If there is sufficient moisture to produce a surface film or the surface appears reflective the runway will be reported WET.'
If I see that a so-called 'wet' runway is not shiny at all, I would call that 'damp' and therefore I would land using 'dry' performance. On short final, the pilots will sometimes have a better view of the runway than anyone, depending on the lighting etc. The trouble is, I'm not sure how legal that is. Most pilots will probably just divert from say LCY if it is declared 'wet' and if they can't land in 'wet' conditions since FODCOM 3/09.
Also I wonder how an A318 will do in 'wet' conditions at LCY?