OP, you knew full well the restrictions on site, IMO the court is not going to attach any weight, or at least insufficient to get you off the hook, to such (IMO) minor issues. In fact if on the one hand and to make one argument you say you knew and then, to make a different argument, you claim you didn't then you might well upset the judge.
b789's tactic is to throw everything in, relevant and, shall we say, less relevant, in order to bluff DCB out of the game.
It has worked in the past, but IMO normally when played earlier in the game. It is not a silver bullet and indeed at least one poster has suggested that for the sums claimed here it wouldn't work anyway.
I'm still baffled by the relationship with your employer and the way you've let this slip. You know far more about this context than your docs could show.
The store manger's email seems unequivocal, so why haven't you gone back for the further help offered. By the way, this email doesn't mention Head Office.
We've no idea who 'Property' is.
Are you saying:
No breach because UKPC were supplied with your VRM which was or should have been included on an 'exempt list' pursuant to an agreement which your employer had with UKPC, and/or
Your employer guaranteed unconditionally to indemnify you against any parking charges
The July email is well after the fact, do you have any contemporaneous correspondence?