In which case, just send the appeal as suggested earlier, with or without the reference to the IAS kangaroo court.
You and we need to see how they decide respond to it considering they don't know who was driving and they can't hold you, the keeper liable unless you want to pay it and admit to being the driver.
If they reject, then we need to see on what grounds. As to a secondary appeal to the IAS, that is up to you. Whilst others on here may believe that there is a remote chance that they'll actually side with the appellant, personally, I believe that with a roughly 4% chance of winning, it's not worth the effort.
Weathering the inevitable storm of debt collection threats is easy as long as you understand that they are just that, threats designed to get the victim to pay up. However, as long as you understand that these debt collectors offer their services on a no-win, no-fee basis and are powerless to actually do anything as they are a third party to the contract the driver is alleged to have breached.
I doubt that this tiddler company would try and litigate. I have not seen anything from them. They are unlikely to try and take this all the way to a hearing as they know they cannot hold the keeper liable.
They either cancel the charge or else try and scare you into paying. If you change address in the next 6 years, just make sure you instruct their DPO to rectify your address for service and to erase your old address.