Thanks for the reply and understand all of the above. The area where I am a little bit stuck in terms of best next steps is how keen I should be to cooperate. I am more than happy to do so as I don't believe I have done anything wrong, I also don't believe they have any way of proving otherwise. However the last thing I'd want is to accidentally say something incriminating by trying to be helpful when it may not be necessary at all. What would the risks be if I just sit tight and say nothing
To give a slightly different take on it from
@AlterEgo:
You're not obliged to respond to anything the railway has sent you: as far as I know they don't have the power to require you to reply to them.
But against that, you don't know what information they have: you can be reasonably certain that they have details of tickets that you have bought online and it's not inconceivable (although in practice fairly unlikely) that they will know about tickets that you have bought over the counter / from a machine if you paid by plastic. You know that they have not stopped you while you have been travelling, but it's my understanding that e-tickets are logged when they are checked, whether at barriers or by an inspector. And you cannot be certain that there isn't CCTV showing you as having made journeys.
It appears that the information the railway have has caused them to suspect that there is a problem with your railway travel. You will know (and you have no obligation to share this with us) whether the railway are right in their suspicion or not.
If the railway's suspicion is wrong, then I would differ from
@AlterEgo in that I would suggest that you should co-operate - you should be in a position to produce further evidence that will confirm that there is nothing for the railway to be concerned about, and so it will be possible to bring their query to a rapid conclusion. This means more hassle for you in producing evidence, but should bring matters to a fairly rapid conclusion - so less stress in the long term.
But it's a bit more complicated if the railway have in fact hit on the true facts, and your travel has been out of order. As people have said, what the railway are asking for is for you to supply evidence that will let them settle matters out of court - which (good news) would prevent them from taking you to court but (bad news) would effectively guarantee that you would have to pay them a settlement. So what will happen if you don't co-operate? In that case, it comes down to whether the railway have sufficient evidence to pursue you through the courts. To do that, in practice they would need enough (and strong enough) evidence to raise a fraud prosecution. That's a fairly high bar for the railway to clear, but you need to be aware that a conviction for fraud is substantially more serious than a conviction for fare dodging.
As I say, only you will know the full facts of your case. But if you have been fare dodging, you will need to make a judgment as to whether it's better to go down the road of providing evidence and almost certainly committing yourself to paying a settlement, or holding the line and playing a high stakes game where you (most likely) walk away without paying anything or else get hit quite hard with a fraud prosecution because it turns out that the railway
do have enough evidence to pursue you.
There's a lot to be said (not least simplicity) for
@AlterEgo's line of not responding. But there are scenarios when a response may be worthwhile.