Too late to do anything about this now as the POPLA code has expired. You can make a formal complaint to NCP which basically tells them to consider the reply that was given in Arkell v Pressdram (1971) and see if they dare try to issue a claim.
NCP are known not to push back too seriously when an official complaint is sent, especially when they know they are on thin ice, as they would be with this PCN. No contract could have been formed with the driver as there has been no consideration period. So, even if the drivers identity has been blabbed or not, they would struggle under litigation.
So, if we work on the presumption, for now, that the drivers identity has is unknown to NCP, a formal complaint to NCP is the next step. However, I would like some reassurance from the OP that they are prepared to fight this all the way before any further effort is put in to the matter.