DO you already have an address where you will be residing abroad? If necessary, can you evidence that address with a utility bill or some other identification? If you can, the easiest way to kill this off would be to identify the driver with the foreign address and that would be the end.
However, as the Notice to Keeper (NtK) is not purporting to rely on PoFA to hold the Keeper liable if the driver is not identified, this would never, ever get near a hearing in a county court small claim. Also, the fact that Gemini is owned by APCOA and APCOA do not litigate anyway.
So, the choices you have are to just completely ignore it and do not respond to anything. As they don't litigate, nothing will or can happen. Any debt collector letters are always ignored anyway as they are powerless to do anything except to try and intimidate the low-hanging fruit on the gullible tree into paying out of ignorance and fear.
Of course, you could be the unlucky first ever person they decide to make a claim against and if they were to (highly unlikely), if a claim was not responded to, you could get a CCJ by default. If there will be someone at the address that can check your post, then it wouldn't be ab issue and we would advise on how to easily defend it with the 99.9% guarantee that it would still never reach a hearing before being struck out or discontinued.
If you can identify the driver as being a foreign resident, then they cannot pursue anything out of jurisdiction. They would soon give up again.
If you want to go through the usual process of appealing, rejection, IAS appeal, rejection, county court claim (extremely low probability), defend, strikeout/discontinuance, then that is available also. In this case it would only go as far as IAS appeal, rejection, useless debt recovery letters and finally silence as they move on, then you can start with the fact that there is no legal obligation on the
known keeper (the recipient of the Notice to Keeper (NtK)) to reveal the identity of the
unknown driver and no inference or assumptions can be made.
The NtK is not compliant with all the requirements of PoFA which means that if the
unknown driver is not identified, they cannot transfer liability for the charge from the
unknown driver to the
known keeper.
Use the following as your appeal. No need to embellish or remove anything from it:
I am the keeper of the vehicle and I dispute your 'parking charge'. I deny any liability or contractual agreement and I will be making a complaint about your predatory conduct to your client landowner.
As your Notice to Keeper (NtK) does not fully comply with ALL the requirements of PoFA 2012, you are unable to hold the keeper of the vehicle liable for the charge. Partial or even substantial compliance is not sufficient. There will be no admission as to who was driving and no inference or assumptions can be drawn. Gemini has relied on contract law allegations of breach against the driver only.
The registered keeper cannot be presumed or inferred to have been the driver, nor pursued under some twisted interpretation of the law of agency. Your NtK can only hold the driver liable. Gemini have no hope should you be so stupid as to try and litigate, so you are urged to save us both a complete waste of time and cancel the PCN.