Andy and the r man,
You might try a product by the name of NOVUS. It comes in three (3) varieties, and maybe more all of which are advertised as Plastic clean and Shine.
NOVUS 1 would clean face shields and windshields of say bugs and grim, etc. NOVUS 2 will take scratches out of plastic, and clear coat on paint. I forget what NOVUS 3 is for. I use NOVUS 1 &2. I would recommend you try NOVUS 2 on your windscreen. It can't hurt. I apply it with my finger, no cloth and gently rub the scratch(s) until gone and then clean with a soft cloth (t-shirt), etc. It may take several applications. If you need one of those headlight buffing kits, you are far beyond Novus!
Good Luck,
Curtis