NCB is reinsurance, so what is happening is your main insurer will claim off the reinsurance company for the difference in the premium that is now applicable as you have lost some of the NCB, so on paper you would be paying the same + or - whatever change the renewal premium would have been but here's the killer, you now have an accident down to you so they'll weight it for that so as redcrx says you will pay more. Depends on he company but they now have you down as "unlucky", ie had one accident therefore more likely to have another.