Keep in mind as well such policy add-ons only apply to that insurer. In the event of a claim, if you go to shop around, full or step-back protection is meaningless to other insurers.
Maybe it's different in Northern Ireland, but I was recently at fault in an accident and claimed through my insurance. The only damage was to the other party's car, not my own and the repair has been settled in the amount of £750. (of course it had to be a BMW I hit!!)
As I was at fault my protected no claims bonus will be stepped back from 9+ years to 4 years. When I put my renewal details through the Compare NI website without declaring the accident and including my 12 years no claims discount that I would have had with no accident, the cheapest quote is £195. (note that I rarely go for the cheapest policy!)
When I submit it with details of the accident and declaring the 4 years stepped back No Claims Discount, the cheapest available quote is £325, about £50 more than I paid last year.
When I submit the same details, but with 0 years no claims discount, the cheapest quote goes up to £425.
So from this in my case, it's clear my premium has gone up due to having an accident, but not by as much if I didn't have protected no claims.