Hi Berkhof:
I'm puzzled at the fact that you say you were pulled over by an unmarked Police vehicle. That just is not possible.
In order to require a vehicle to stop, a Police vehicle has to be of the marked variety and fitted with "blues + twos", and the Officer(s) have to be in uniform.
The only way that this could have happened as you described would have been if they had followed you until you stopped, then approached you. The Officer(s), though, would still have been required to be uniformed.
If he told you that you'd been pulled over for speeding, but was prepared to "waive" that offence, he was waffling and I'll tell you why. Simply because he wouldn't have had the right equipment in his vehicle to prove the offence anyway, owing to the fact thah his was an unmarked car. He wasn't doing you any favours. The only other way he could have tried to do you for speeding would have involved him having his own car calibrated by the traffic cops at a later stage which would have been a pain in the butt to have done.
He would at some point have done the PNC check which allegedly then showed up your car as being uninsured. This may have been out of date information, or else he was, again, waffling because you only have his word, right?
Could this be what really happened? Did he actually report you for anything or issue you with a "producer"?