I have sanded and polished one, quite a lot of sanding 800 grit to get the film off and then 1500, 2000, 3000 then polish it's come up nice and smooth and shiny but I think it now needs something or somehow polishing on the inside
I used the Autoglym kit on my Chrysler headlights which were really badly discoloured. Started with fear and trepidation, but was really easy and came up beautifully.
If by "film" you mean the transparent lacquer on the headlight covers, it can be easily removed with acetone. Nail polish remover should also work fine.
There may be different products available, so test it first to see if it does not react with the plastic (for example under the headlight edge).
I used Farecla G3 on my wife's Saab headlight which had been picked up on its MOT.
Farecla G3 is a rubbing compound slightly better than T Cut, which can be used.
Farecla is available at most car accessory shops.
I wouldn't use sandpaper ... I tried it first and ended up with so many scratches on the headlight that it looked opaque ... The G3 applied with a cloth did the trick and took just minutes.