From another Old geezer.
Wickes good idea leaflet states polycarbonate sheeting should only be cleaned with water and mild detergent applied with clean sponge and soft cloth.
I use my jet washer set for shampoo and rub over with very soft broom. Then jet rinse at low setting. If you haven't a jet washer you can get attachments for a hose that takes detergent.
Don't use abrasive creams. If stained check out at Wickes conservatory sales see if they can advise.
Charlie
March 2010