I use Meguairs PlastX polish - really cleaned my old IS head lamps and fog lights a treat - took a few goes as it is not very "cutting" but bottled out of the Brasso route as I felt this was too abrasive - cribbed this from the web for info:
Meguiars PlastX Clear Plastic Cleaner & Polish G12310
This easy to use, rich gel formula quickly restores optical clarity to both rigid and flexible clear plastics. Cutting-edge advancements in Meguiar’s exclusive Microscopic Diminishing Abrasive Technology (MDAT) easily removes oxidation, chemical degradation, contamination, stains and light surface scratches. Plastx also contains long lasting durable protection to keep your plastics clear and beautiful longer. PlastX is non-toxic and does not contain harsh solvents.