You will need to await the reply from the Train Company but it seems quite likely they may opt to prosecute you under either
the Regulation of Railways Act Section 5 or Railway Byelaw 18.
The next likely step will be that they will write to you asking for your version of events. It is up to you how you respond but it would be wise to tell the truth at this stage as lying is likely to make the situation worse. You can also consider replying stating that you're very sorry for your mistake, that you will never do so again, that you are willing to pay the fare outstanding and any administration costs they've inccured.
In our experience replying along the lines of the above may sometimes (but not always) enable you to avoid court and a potential criminal record.
If the TOC decide to prosecute you then you have a few options:
1) Defend your case in court by pleading not guilty. You'll need to be able to defeat the evidence that the prosecution will bring against you. Further if you're found guilty you'll not only face a fine and potentially a criminal record but also the other sides costs (you would also lose the advantage in sentencing of an early guilty plea potentially reducing the fine).
2) Plead guilty and accept a fine and potential criminal record.
3) Write directly to the TOC apologising for your actions and offering to pay the fare outstanding and whatever costs they've incurred so far. They may opt to accept a payment from you directly and avoid court or they may wish to proceed to court.
Finally, and especially if they do take you to court, you should strongly consider seeking professional legal advice even if it's only a 30 minute free consultation. Whilst specialists in railway law are available they are not common and charge a great deal for their services. However, a local firm dealing in criminal law defence should be able to provide adequate assistance.
You may wish to consult the
Legal section of our
Ticketing Guide for more information and with particular reference to
this section and
this section.