I am a windscreen fitter by trade and deal with the insurance companies everyday, so here's the dinfinitive bottom line....

If you have a fully comp policy with glass cover, then you are entitled to have any piece of glass changed where you pay the excess (which dependant of insuranc company, could be £50, £60, £75 and a few are now £100) and the insurance company picks up the rest of the tab... This does not affect your NCB as it is a seperate thing, independant of your vehicle policy.

In regard to windscreen stone chip repair, provided the chip is repairable (two critirea : size dependant for both the physical repair and also size dependant for MoT) then your insurance company picks up the whole tab for the repair and the policy holder pays nothing.

HTH's