We don’t have templates for “I don’t want to pay” appeals.
From what you’ve said so far, the driver parked in a car park with clear signs limiting the parking period to 30 minutes, and entered into a contract according to the terms on the signs. The driver then parked for significantly longer than the free period, significantly more than 10 minutes longer as defined in the free “grace period” on top of the base period.
You’ve not given any other reasons for why the driver parked for longer than allowed.
Bottom line is that they’re entitled to pursue the driver for breach of contract, and use PoFA 2012 to transfer liability to the registered keeper. Horizon seem to be reasonably compliant with its requirements, unlike others.
You rightly approached Tesco but they were unhelpful.
Unless you have a defence you can construct to a likely county court claim, I’m not sure what else we can offer. You can tell Tesco that you won’t be shopping there again, of course.
Most appeals get rejected "after careful consideration" anyway, so you can throw in a generic "not compliant with PoFA 2012" appeal if you want, but it'll be rejected and you'll go down the well-trodden path to a court claim.