How do you propose to evidence the mitigating circumstances? Their Notice to Keeper (NtK) is PoFA compliant and so, even if they do not know the drivers identity, they can transfer liability for the charge to the Keeper.
The charge is for an alleged breach of contract by the driver. Did the driver breach the contract? In simple terms... yes. Can you fight it? Yes... but...
You can submit an appeal as the registered keeper explaining what happened, and it’s worth doing to show you’ve tried to resolve the matter reasonably. However, in reality, any initial appeal is always rejected and the odds of an IAS appeal being successful are as likely as winning the lottery. If the parking company won't cancel the charge based on mitigation like a medical emergency, then you can bet that the IAS won't either.
After the appeals are rejected, you will start getting letters from debt collectors. These can be safely ignored, as they have no power to take action. All debt collectors can do is try and persuade the low-hanging fruit on the gullible tree to pay up out of ignorance and fear. The only time you need to respond is if you receive a Letter of Claim (LoC) or an N1SDT County Court claim form.
If it goes to litigation (likely), what happens next depends heavily on which bulk litigation firm is handling the claim for the parking company. Some firms, like DCB Legal, Gladstones, and Moorside Legal, issue a lot of claims but often drop the case before it reaches a hearing, especially if the defendant puts up a solid defence or challenges their conduct. In those cases, there's a good chance the matter won’t go all the way to court.
On the other hand, firms like BW Legal or QDR Solicitors are more likely to pursue the claim all the way to a hearing. If it gets that far, a court will generally look at whether the terms of the parking contract were clearly displayed and whether they were breached. If you paid for parking but overstayed, and the grace period doesn’t cover it, then unless you have a strong legal argument (such as unclear signage, unfair terms, or procedural errors by the claimant), the court may find in their favour. Courts may accept personal mitigation as a reason not to pay if the terms were breached.
So, while you can and should appeal, the most likely outcome is that the charge won’t be cancelled unless you either win on legal grounds later or the claim is dropped before it gets to a hearing.