If damage is not on purpose, the loss is still payable. As consumer, the duty is to proof the loss and then it is up to the insurer to determine whether loss is payable or not. If not, insurer will have to give reason why and the onus shift back to consumer to proof otherwise.

Well, for windscreen you can get separate windscreen cover for your comprehensive policy by paying an extra premium. If the windscreen is broken/chipped you can still claim from the insurer. However, if no extra premium is paid but you still intend to make a claim, the downside is that you lose your NCD.