Ok as closure on this , windscreen fitter came today ,, words were exchanged as to cause of damage ( that was quite extensive under the cowling !) with him siting a blunt force , tennis ball , football etc , and me claiming , that any trauma would leave a mark on the plastic cowl ( I work with plastics for a living ), any how , we agreed to differ , he called his manager , I got a new screen foc , and blame was put on .... bad connection to windscreen heater , but tbh , and whether it's connected or not , I'm sure I heard a little ping , when I first used the screen heater After the last screen was fitted ,not sure if I imagined this or not , but the damage seemed to be centred on one of the cable entry points , I wonder if a localised hot spot could do this ? Interesting ........ discuss