in their email they said they are now looking to prosecute under the fraud act which has no deadline on it?
It's worth thinking about how realistic this threat is. In brief, I don't think it's very likely.
The thing is, what is being suggested is a criminal prosecution. That means that the prosecution would have to show 'beyond reasonable doubt' that your bf had used Railcard tickets when he didn't have a Railcard. That's two hurdles for the prosecution to get over:
- did he have a Railcard? It's for the prosecution to prove that he didn't rather than for your bf to prove that he did. And since there's no obligation for your bf to have kept an old Railcard or to have bought one in a traceable way that's quite difficult for the prosecution - unless your bf helps them by admitting that he didn't have a Railcard.
- did he use the tickets that he bought? Buying tickets with a Railcard that you don't hold isn't an offence - but using them is. I will say that this is a weaker point in that a prosecutor might reasonably ask why someone was buying tickets that they couldn't use (there are good reasons if you buy tickets for friends and family who DO have Railcards - but you should only say that if it's true), but that's still no reason for your bf to help the prosecution do their job for them.
While it would be open for Chiltern to go through the civil courts to recover the fares they think they are owed (that has a lower standard of proof - whose story is more likely to be true? That gets around the problem of buying tickets as it could reasonably be assumed that they were bought by your bf for use by your bf but still leaves the problem that it's not unreasonable to have thrown away old Railcards) that would still be a costly risk for the railway to take - there's no guarantee that they would win, and if they lose they have lost their costs.
Realistically, Chiltern are trying it on. They're out of time for a magistrate's court case and are abusing information they have picked up from this forum. Ignore them and don't help them to take money away from your bf.