Despite the fact that Chiltern are clearly rigorous on ticket infringements is there not a reasonable probability that the staff member stopped the OP, was suspicious of their ticket, questioned them (to which the OP made no specific admission that the staff could then use to support any potential prosecution threat and there is no other supporting evidence of their evasion, like being caught on the train), took some evidence from the ticket just in case their revenue protection back office team might be interested but also as a low level 'warning' to the OP - which from what has been said on here has worked in terms of the OPs future intended behaviour.
The advice has to be
- 100% avoid doing this or any other dodgy ticket activity again
- AND watch out in case you hear from the railway for at least the next 6 months - ensure post is checked, esp if move address
- head back here for advice if the railway or their agents (TIL probably) make contact about this.