PVCU solvent cleaner - using it!

I usually put it on a rag and rub it in and polish it off. Be careful with it. It is abrasive and will take the gloss off the frame. Have you tried using cream cleaner and a lot of elbow grease both to remove the staining and to polish the frame up if you do use the solvent cleaner. If you have a power drill it may be worth your while springing for a sissal mop to save on the elbow grease.

One final thought, how old are the windows and what colour is the staining. Even the most modern UPVC will discolour in sublight eventually (We're talking 20 years plus here). You're not trying to clean off yellow or pink discolouration, are you?

Have you tried turps thats a wonderful cleaner? Usually CIF or any cheap cream cleaner does the trick with a bit of elbow grease.

I have also tried those UVPC cleaners from Screwfix but I didnt leave it on

I found a good cleaner that may or may not help, never tried it on uvpc but its brilliant for hobs, and log burners to remove tar, I wondered if that may do the trick it isnt abrasive, or toxic ist an old fashioned cleaner, its called Bar Keepers friend not many places sell it but Sainsburys does its about £2.50 and you need very little on a wet cloth, it last ages

http://www.homecareproducts.co.uk/tips.htm

Actually Hobbrite does it in link above

Cleans:
UPVC Window frames.
Metal alloy wheels.
Pushchair wheels.
Plastic garden furniture.
Ceramic hair straighteners.
Gets rid of black scuffmarks on white trainers.

For a really stubborn stain or scratch, use fine grit (400) sandpaper in a rotary sander and polish up with a sissal mop and cream cleaner. Don't sand to deep, the dip will catch the light and be very, very obvious.