In reply to Bouldering Ben:
Unfortunately there are still selfish climbers around who persist on climbing on wet sandstone in spite of the publicity given to this subject.
A couple of years ago I was walking past Stone Farm Rocks in the rain when I came across a so called "instructor" instructing a group there. I asked him, politely, not to carry on, but he continued. It was a terrible example to set to newcomers to our sport - shame on him.