Seriously, don't claim if you can help it. Glass claims doesn't effect your NCB.
I lost 4 years NCB a while ago and am still regretting it now, went a long way out of my way to avoid it but the other guy was a cunt and put a claim for whiplash in even tho I hit him at less than 10mph and did zero damage to his car. Worked for the AA as well - arsehole association IMHO