Go easy with the acetone cos it softens the plastic. Agree that it works though as I'v used trade strength uPVC cleaner...the stuff window fitters use and that works well and has acetone in it. Always wash it of well afterwards though and give them a coat of polish to seal the surface. Keeps the dirt out.
Ralph's idea has won.
Tryd it out yesterday with astonishingly good results. Spray oven cleaner and a scouring pad brought them up like new, and I meen like new.
Thanks for the tip Ralph.
Ian