I doubt that whatever you put in your appeal will result in a win at this stage. What is required is for Britannia to provide you with a POPLA code where this is likely to be won.
As the NtH was sent to the driver, it should be the driver that responds. The keeper no longer has any liability and that has been acknowledged.
Whilst I don’t disagree with
@H C Andersen about the terminology about an NtD which I should have referred to so solely as a PCN, I think that pointing out that as an NtH, there is no advantage highlighting the reasons that it fails PoFA because that is only used to show that the keeper cannot be liable and we have already established that keeper liability has been transferred anyway.
Britannia have failed to follow the correct procedure to be able to hold the driver liable because they have issued the wrong type of invoice. Any appeal should simply point out that Britannia have failed to follow the required procedure and should simply cancel the PCN or issue you with a POPLA code.
I don’t think there is any mileage in detailing their mistake at this stage. Just get the POPLA code and have them deal with it.