No rush to appeal, as long as you do so before the deadline.
If it does all go pear shaped, the NTK says
"If your appeal is declined, you will be given the right to pay the rate applicable when the appeal was made, for a further 14 days".
So if I want, in the event of getting nowhere, to only pay £50, tomorrow is the 14th day after the notice was issued, don't I have to appeal by then?
as the overstay was due to delays at their checkouts
Aside from any technical PoFA deficiencies, this detail could support an argument that the contract was frustrated. When you say delays at their checkouts, was this due to some sort of technical failure, or was it just that they were busy and the driver didn't allow enough time to get through them before the maximum stay expired?
They were not especially busy, and the driver allowed what would normally have been enough time, but was unfortunate to be significantly delayed because the person in front of them was elderly, and the checkout operator was packing every item into bags for them, one item at a time, and then loading full bags into trolleys (the customer had two).
I'm pretty hopeful that Waitrose will intercede, but the manager is away, and I don't know if anybody will deal with it in his absence, so my initial thought on the appeal was just to stop the clock for a bit.