The byelaws specify actions by "Qperator" or "Authorised Person". If they have no uniform (or external identification badge, etc.) , are passengers entitled to ask them to prove that they are "authorised persons" ?
There's a distinct bias in most of this thread, (in this case 'them' and a requirement to 'prove') in which I'll try remain balanced.
Yes. A passenger is not denied any question to a person employed by 'the Railways' (whether employed by a TOC, NR, BTP or a contractor). The person employed by the Railways is not put to proof by such a question - they are not obliged to 'prove' anything, to any standard of 'proof'.
In response to such a question, I'd expect the prospect of a reluctance, or even indignation, to be equal, whether it is the passenger asking the employee to prove their identity, or the employee asking the passenger to prove their identity.
There have, in the past, been occasions where people have been conned out of their tickets by persons claiming to be a "ticket collector".
I do recall one particular 'character'. But that is far less of a hazard than the number of railway Operators who are conned out of their fares daily, by passengers claiming some falsehood, and often resisting providing their identity while happily travelling without paying.
If it wasn't for the widespread practice of opportunist fare evasion, then there wouldn't be Revenue Protection personnel (directly employed or contracted) in such large numbers on our railways.
I am surprised at the degree of anti-railway opinion on this forum which seems to overlook this underlying cause of much of what is disliked: Fare Evasion.