For heavens sake, I hope you did not blab the drivers identity when you "spoke" with APCOA! What a guaranteed way to figuratively blow both feet off with a single shot!
APCOA "Penalty Notices" are fake and illegal instruments of fraud and you should report them to the police (NOT Action Fraud).
They are designed to intimidate the recipient into believing that they have the authority to prosecute a statutory criminal offence when they have none. Their Penalty Notice (PN) is a speculative invoice from an unregulated private parking firm who have no "authority" to prosecute anything yet use language that is prohibited in civil contract law.
APCOA will NEVER, EVER, EVER try and prosecute one of their fake PNs in the magistrates court as a criminal breach of the Railway Byelaws. Even if they ever did (and they won't) they would have to prove beyond a reasonable doubt that the person they were prosecuting was the liable party. As there is no legal obligation on the Keeper of the vehicle to identify the driver and they should decline to do so, there is no way APCOA can prove their case. They will mendaciously waffle on about it being the "owner" who can be liable under Railway Byelaw 14.4 but there is no register of "owners". They will then try and bamboozle you into thinking that the Registered Keeper must be the "owner". However, if you look at your V5C registration document, you will see very clearly and boldly written on the front of the document that it is not to be used as proof of ownership.
I can go on and on but I see so many gullible people that simply poop their pants at the through of a "criminal prosecution" in the magistrates court simply pay up when there is absolutely no way whatsoever that they could be prosecuted. APCOA will then set the debt recovery agents to send letters threaten in a claim in the county court for what is supposed to be a statutory penalty!!!! Suddenly they try to conflate a PN into a Parking Charge Notice (PCN) under civil contract law.
Even if you did absolutely nothing and ignored ALL future correspondence, APCOA will still never litigate the matter. They are benign because they know they are going to make so much more money from all the low-hanging fruit on the gullible tree who will pay up out of ignorance and fear.
If the PN were real, it would not be possible to prosecute after 6 months. It is not real and they will not/cannot prosecute a fake PN. They will try and threaten to sue you under civil contract law, and again, cannot actually do so because it would be thrown out at the first hurdle.
APCOA does not have any contractual authority from the Train Operating Company to issue PNs.
You can read up on the reasoning here:
Why APCOA have no authority to issue Penalty Notices under railway bylawsYou should also read this thread, whilst it applies to SABA rather than APCOA, it is fully relevant to this and any other "penalty" issued by an unregulated private parking firm:
Saba Parking Services - Railway parking site - debt collector before initial notice?So, I advise that you follow the advice given in that second link about SABA and you make contact with the police, not the useless Action Fraud, and report APCOA for fraud by false representation (Fraud Act 2006, s.2),
Contact your MP, report APCOA to the DVLA and your local police force economic crime unit, as per the examples in the thread linked above.
You will never pay a penny to this firm that operates outside of the law.