In reply to Raoul Fearnley:
Last year, I was organizing a course for me and my friends in Bowles, so I gave Bowles a call asking about potential rain (forcasts were looking bad). They said rain was not a problem and the course wouldn't be canceled. We were lucky on that day as rock wasn't too wet and no rain at all but looking back, I would rather cancel or move session but probably lose paid money.
We went to Bowles last Saturday and the rock was good to climb (not everything). It was sunny and cold day and we didn't climb anything that looked and felt wet for both reasons - damaging the rock and rather unpleasant climb. This Friday we are going to Harrison's. If no go, we have always a backup plan - indoor gym in Tunbridge Wells which isn't too far. Either way, we gonna climb something