Opaque headlight

Has anyone had their headlight become opaque with age, and is there a known remedy? I've just bought this Roomster and the driver's side lamp has a noticeable haziness or opaque quality which the passenger side headlight unit does not. Ive had cars do this in the past and have sorted it with a good polishing as the deterioration was external, but this does not appear to be the here. I don't think its condensation either although I suppose it could be a residue from years of misting.

Is it possible to gain easy access to the inner face of the headlamps? I know with some headlamp units you can heat them up and split them in an oven.

Cheers

Ben