Not heavy rain, no I don't. I don't believe the customers like it either
someone will be along soon saying ALL my custys love me cleaning in all weathers 

we clean in the rain, we like to offer regular service to all customers not working in the rain would affect this especially with the UK weather the way it is, only weather we do not work in is thunder and lighting, high wind or when i mean it unsafe to work.
if we didnt clean in the rain I would either have to not pay my staff or pay it out of my profits and neither am I willing to do when there is no valid reason not too.
Yesterday it was hammering it down and we had a day of new cleans aswell as regular customers, customer may not like it if they don't understand what you do or why you do it, educating people is the key here.