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In addition to what you've shared it would be useful to see:
- The Notice to Driver that was on the windscreen
- Photos of the signage at the site, including ones showing their layout and prominence
- If any appeal has thus far been submitted
It would be ideal if your friend could post here himself. Where people post on behalf of someone they know, it often has a tendency to turn into Chinese Whispers.
No appeal has been submitted yet but he did call them up and identify himself as the registered keeper, asking them for the original notice which was later found.
Unfortunately google maps doesn't show the signage in detail nor does it go further into the estate. On google maps I can barely make out it says "PRIVATE LAND PERMIT HOLDERS" on the sign into the road.
There was no notice on the windscreen. The NTK was received in the post, the entry and exit times were caught on ANPR. The driver stayed in the car for around 26 minutes then left.
I will upload the first notice shortly, I was told it was received sometime in January. Let me know if this is not enough information to make an appeal, I will let him know as he has left it quite late.