It is possible to polish polycarbonate, search the web for restoration of polycarbonate headlights. I am about to do this on my car and will report the results.
Based on experience with polycarbonate you’ll get results that are plenty OK for headlights but not good enough for a windscreen. Acrylic is much harder (also more brittle and not as strong) so aircraft windscreens are much easier in this regard, notwithstanding the potential problems with distortion.
Meguiars link and similar companies make good polish once you get the surface flat and uniform with wet sanding down to 2000 grit or so. I once did a badly scratched motorcycle windshield starting with a file but don’t use anything coarser than necessary because each step finer is lot of work. You can then use several grades of polish working toward the final polished finish after sanding. It’s important not to put deep scratches in the surface in the initial steps, uniformity at every stage minimizes the work at the next finer stage.
Thanks guys.
the “milky” one is one side window only. So that one will need replacement at some stage.
The windscreen on the pax side suffered some bruising from an old cover. That would be the one which might be repairable with some of those methods.
Some good advice here, thanks.
What you have to be very careful with is not creating flat surfaces, or generally surfaces whose curvature differs from the surroundings. You get weird optical effects then.
Peter wrote:
What you have to be very careful with is not creating flat surfaces, or generally surfaces whose curvature differs from the surroundings. You get weird optical effects then.
Yes, that is indeed a big issue. Thankfully the affected windows are pretty straight.
Just as bad 
