Fenwicks windoweze you can get from any caravan shop or Halfords you can also use Brasso both work fine.Just use a soft cloth to apply and then polish off.
i would have a go at removing any bad scratch, but every window on my van has scratches, its plastic, so you will never have them scratch free, pull the nets down?
If you have seriously deep scratches then try your local caravan dealership. Many of them have buffing machines that can take out marks that you will never remove with hours of rubbing. The cost ( at least in mycase) was very cheap compared with the irritation of looking at it all the time.