I know someone was asking about this recently. Just found this video which covers the procedure and seems to have reasonable results...
Is a polishing mop necessary, can this be done by hand and a bit of elbow grease Are there marking on the cover?
did mine with some t-cut and an old rag, came up a treat. My dads 206 lights were very bad so i did them with some wet 1200 grit then followed with t-cut. Both cars looked factory fresh.
they really were bad: yellowed, covered in stone chips, rough to touch. The 1200 grit took them back to a light haze and the t-cut bought them up lovely. Alot of the kits you buy for headlight restoration come with a small piece of 1000 grit so using some wet 1200 was fine. It barely leaves a mark on clear-coat so the hard plastic of a headlamp would recover fine.
Megs do a headlight restoration kit now, i bought one but just not got round to doing it. The guy at my garage is going to have a do with it when zeddy goes in next.