If you want to challenge a PCN you should contact the council that issued it as soon as possible. You should refer to the PCN number, what happened, any information relevant to the issue of the PCN and why you believe you should not have to pay it. This is often known as an informal challenge.
Always send copies of evidence rather than the originals.
The council will then decide whether or not to cancel the PCN. If the council does cancel it, you have to pay nothing. If it does not cancel it then you can continue through the challenge process or pay it - you only have to pay half the amount if you pay before the end of the period of 14 days beginning with the date of service of the PCN.
(Please note, challenging the PCN before the end of the 14 day period may, in some cases freeze the discounted rate but this is not always the case - you need to check with your individual council) If you are unable to respond in time (e.g., you were on holiday or the PCN was delayed in the post), you should inform the council immediately.
If the driver issued with the PCN is not the vehicle owner they should give the owner copies of all letters or emails sent to the council.
If a council decides not to cancel a PCN it will send a Notice to Owner (NTO) to the vehicle owner - presumed to be the person the DVLA has on its records as the registered keeper of the vehicle. An NTO will also be sent if the council has not had payment or any contact from the driver before the end of the period of 28 days beginning with the date of service of the PCN.
The NTO includes a form that allows you to formally challenge the council about the PCN.