UPDATE -- GOOD NEWS
I just got a reply to my SAR, with photos and everything.
It refers to a parking offence from 30th May 2019 (!), involving my _previous_ car, and was sent to my _last but one_ address.
The good news is, the photos show that it was not my car!
It's the same make and model, but appears to be grey or silver instead of white.
The front plate has an F that an AI could mistake for a P, because of a retaining bolthead.
But the rear plate clearly shows an F where my reg number has a P.
So who should I reply to, and how?