NCB and protection thereof works like this, I will use arbitrary figures as an illustration. Say you have 70% NCB and the base premium is £100, then you will pay £30 + a small amount to re insure against the NCB, say £5 so you will pay £35 for £105 worth of insurance, your £5 is protecting you for a potential hike of £70. Now you claim so you lose the NCB but your NCBP now comes into play and at renewal you get the payout of £65 but that is against the original premium of £100, so now they add on the price rise for that year and the price rise because you are now a higher risk, say £10 + another £5. So the new base premium is £115, less your reinsurance payout of £65 = £50, that's your new premium. Which looks like a hike and it is NCBP only protects the NCB amount from the preceding year.