I think this is the last time I'll post on here. People seem to want to make thinks more complicated than they are.
Yes, it could be pro-active and helpful to write in an ideal world, but we don't live in that utopian place. The processing agency IRCAS or RPSS dependent on TOC may close the file, but they are only concerned with the throughput of notices for which they get paid. The message will NOT get relayed to every railway guard/conductor/inspector on the network and the next time Mr or Mrs X gets caught the cycle starts again. It's no good running to the Police, they will say there is nothing they can do, so I'm afraid that we have to deal with the real world.
If the OP is not the named person, they are not threatening to prosecute him.
They are threatening to prosecute an unknown person at his address. No problem, they cannot prosecute an address and there is no such person known at that address
If a larger envelope addressed to the same name, which is likely to be a Summons, turns up, mark it 'NOT KNOWN - RETURN TO SENDER AS PREVIOUSLY DONE ON XXXXXX DATE'.
You can be assured that the TOC prosecutor is going to have some difficult questions to answer about identity checks when they face the Legal Advisor at the Magistrates Court.
He or she will pass that 'tongue-lashing' down the line to IRCAS or RPSS
We don't any of us like being made fools of, do we?