What happens to car insurance after a fault accident?

No-claims discount and premium are not the same thing

Protected no-claims discount can preserve the discount percentage in certain circumstances, but it doesn't freeze the underlying premium. The renewal price can still change.

You may have to declare the incident elsewhere

When comparing policies, give the claim information requested by the new insurer. That can include incidents that did not result in a payment, depending on the question.

Check how the claim is recorded. If the status changes later because costs are recovered, ask the insurer to update the claim record. Keep confirmation, particularly if you are shopping around before databases have caught up.

One claim does not produce one predictable increase

Insurers rate claims differently. The cost depends on the circumstances alongside the rest of your risk, so there is no reliable universal percentage increase after an accident.