In reply to Pottsy84:
Southern Sandstone needs a long time to fully dry out. With the rock being so soft it is porous and it's not just a case of the surface needing to dry, the rock it's self needs to dry out. Plus the sheltered nature of many of the crags lead them to be slow drying and suffer with seepage.
Add that to quite how easily damaged the rock is (particularly when wet), and some of the sensitive access arrangements that exist, I really wouldn't bother in the winter months.
No doubt you'll get someone telling you that they've climbed on it after a few dry days in the winter and it was fine and I know how tempting it is when it is the only way you can scratch the outdoor climbing itch in the SE, but a bit of restraint will mean it's there to climb in the drier months for many years to come.