> It was my insurer who advised I went and dealt direct with his insurer - hence my insurer has no costs to recover and hence my insurance record with them remains unblemished - They confirmed this.
Wrong; your NCB remains unaffected. Your base premium will go up, just like your base premium goes up if you have speeding fines even though there is no direct cost to your insurer. It's going to cost you several hundred pounds over the next 5 years.
Even if you have one of those rare insurers who don't jack your premium up, if you ever want to change insurer in the next 5 years, your premium will be going up with the next insurer.
If you want to check the effect of your non-fault claim, you can go to an online comparison site like confused.com or gocompare.com and plug in your details with and without the non-fault claim. This separates out the effect of the claim with the general rise in premiums.
> My car was damaged and had to be repaired. The culprit had no interest (understandably) in settling outside of the insurance process.
You would be better off eating the GBP90 yourself if you were happy with the GBP90 repair; or telling the other party that in the interests of good intra-office relations, they should give you GBP90 out of their own pocket. This is going to cost you a lot more than 90 pounds over the next 5 years.