Hi Ally,
You can get a rubbing compound from the internet for refurbishing car headlamps, I did my mH windows which are very scratched, it doesn't remove the scratches but makes the windows very clean. After a coat of car polish seals the scratches and keeps them clear for a little longer.
I'm told there is also a compound for sale in caravan accessory shops that will do the same job.
Good Luck
Bill