You don't mention the circumstances that led up to the PCN being issued, but if you feel you have grounds to appeal the charge then you can do so.

Assuming it was issued by a company rather than a local council warden, you need to check if the company operating the car park is a member of a trade body, either the British Parking Association (BPA) or International Parking Community. If this is the case, you should start by appealing the charge with the company who issued the ticket first. Write to them, giving them the ticket number, your registration number, the date the ticket was issued and explain why you think the charge is not applicable. Include any evidence you have available to evidence this. You do not need to explain who the driver was, just that you are the owner of the vehicle. If this is not successful you can then appeal to the relevant trade body using the same process.

If the company is not part of a trade body, you need to write to the company in the same way and explain that you will not be paying the charge. Again, do not say who the driver was, only that you are the registered keeper, because this means you can deny responsibility for being the driver at the time and cannot be pursued for the charge. Remember to include all the available evidence you have and explain why you think the charge is unfair and will not be paid.

The crucial point to remember is that because this occurred on private land, it is not technically a 'parking ticket' but an invoice. These companies do not have a right to fine you, only to send you an invoice based on what they see as a breach of contract. You can also complain to the owner of the land if you are not successful.