Got caught on bus by not paying bus fare, surprisingly now get a refund cheque 6 months later?!?

I think that with an oyster card which is valid, it is difficult to prove the guilt of the person concerned. Where a person shows an out of date p or a forged ticket (there used to be a lot of those around in London, produced by people adept at cutting and pasting), then you have something to brandish in front of the magistrates. Where there was no ticket at all, then the guilty party either has to plead guilty or produce a ticket to exculpate himself (which he can't do, as if he had been in a position to do that he wouldn't have been charged in the first place). But how do you demonstrate in court that any oyster card has not been swiped? Maybe this is the problem?