The keeper needs to make a representation which makes clear that the representation IS the appeal and, therefore, they must uphold the appeal or reject it and provide a POPLA code.
No need to faff about chewing the technicalities over at this stage.
This will 99% win at POPLA.
I'd suggest the following;
Thank you for your last email.
I have noted the representations which you have made.
Please consider that this email is my formal appeal.
Your note relating to the keeper being liable (via assumption) under contract law is utter nonsense and I am submitting this as evidence to the CMA as your statement clearly demonstrates your intention to mislead a consumer - additionally, your statement could lead a consumer (the keeper) to conduct a financial transaction with you.
This unacceptable behaviour is clearly highlighted in the recent open letter (to the parking industry) from the CMA.
For the purposes of clarity;
I am the vehicle keeper and, in the circumstance, there is no legal or contractual requirement for me to reveal the driver.
As per VCS Ltd v Edward - No adverse conclusion can be drawn from a keeper saying nothing when the law does not require the keeper to say anything.
Your choices are;
1. Save time, money and further resources by cancelling this PCN
OR
2. Reject my appeal, waste more time and money by providing a POPLA code so I can submit a slam-dunk appeal.
I am sorry that I cannot help you further.
Best wishes,
xxxxxx xxxxxxxx