Like a good citizen I told my new car insurers about the incident I had relatively recently, despite not having heard anything from the 3rd party on the matter. The new insurers have to take this at worst case to protect themselves, meaning I've now got an 'at fault' claim against me and my premium has increased by half again. There doesn't appear to be any length of time that the 3rd party has to make a claim within, except that incidents are kept on the insurers shared database for 3 years. So I'm guilty until proven innocent, and may have 3 years with this 'at fault' claim on my record when in reality no one may even claim anything!
Oh, but luckily for me, they're not going to dock my 'no claims' by 2 years (which would actually be pretty bad for my premium).
I should have just kept my big mouth shut until (if) someone squealed about a claim.
Hats off to the New Sales Manager at Admiral though. He spent 30 minutes going through how it all works and made fleecing me an almost pleasant experience.