There are a number of glass scratch removal kits on ebay. Mostly comprising of Cerium Oxide Powder and drill adapters with polishing pads. Also available from Frost (frost.co.uk).
https://www.frost.co.uk/glass-polishing-kit-windscreen-glass-scratch-glazed-repair/ I have used them a number of times with good success. When I purchased my Plus 8 it had fairly deep gouges in the windscreen which I polished out. Main points are to mask off the bodywork as the abrasive polish can be thrown around from the rotating pad, and take it slowly as the polishing process can heat the glass up.
