Just to add, there’s a remarkably similar situation from a while back in the press.
Commuter exploited Oyster card loophole, paying only £7.20 for travel between East Sussex and London Bridge over five years
www.theguardian.com
Essentially a professional (like you, with a regulatory body), was only buying tickets from what I can gather for a small part of his journey.
Seems to have been caught in similar circumstances too, after a period of intelligence gathering.
Only real difference is the length and value. Arguably if someone fiddling £43,000 can get a settlement, you certainly can.
The only caveat I would add to this, however, is that even with a settlement, you may be required to tell your employer or regulator that you’ve been involved in a criminal investigation, and the outcome was XYZ - even if it doesn’t result in a prosecution. You’ve still been interviewed under caution as a suspect of a fraud / financial crime against the railway, and a criminal investigation is now ongoing. The fact the police are (or were) involved is likely to also be an important factor.
The above case still ended up in a career ban for the chap once the regulator found out, even though he paid a settlement.
Financial Conduct Authority says conduct of former Blackrock MD Jonathan Paul Burrows fell short of the standards expected in the City
www.theguardian.com
I would seriously consider speaking to a union rep or solicitor, with a view to approaching your regulator, because I think if your regulator ever was to find out, they’d probably treat you more harshly for not telling them, then the effect of admitting your wrongdoing in the first place.
As the above story says, the regulator took a view that not disclosing the case to his employer made the matter more serious.
You can, of course, take the chance that they’ll never find out- but I find with considerable experience, it only takes an unhappy divorce, family dispute etc for an anonymous tip to arrive, so you really need to weigh everything up.
On the face of what you’ve said, I would personally tell my employer sooner rather than later, and express deep remorse, and explain you are doing everything possible to make things right. I would expect you to face disciplinary action, perhaps even suspension temporarily, but I very much doubt you’d lose your job. Honesty and holding your hands up counts for an awful lot.