the passenger's word that the machine is out-of-order is unlikely to be accepted by them or any court.
As previously stated, I strongly disagree. If you were referring to the passenger's prospects in civil proceedings then perhaps you would be nearer the truth, seeing as the claimant merely has to prove their case on the balance of probabilities (51+% likely). But for criminal proceedings, given the bar is 'beyond all reasonable doubt' (i.e. somewhere north of 90% likely), a consistent allegation of the non-functionality of the ticket machine (as here), without strong and independent evidence to the contrary, is not going to suffice for guilt to be found by a reasonable person.
It was fortunate that I did succeed in buying a ticket on the train, because there were RPIs waiting in the underpass at Queen Street where I changed trains.
It might have saved you some time but I would like to hope that not all TIL-reporting RPIs are as poor at their jobs as the one(s) who the OP came across were. It's a basic tenet of ticketing law (and, frankly, common sense) that you can't expect someone to use facilities that don't, for all intents and purposes, exist because they're not working. With photo evidence there is no way anyone can claim you're fibbing either.
I took a photo of the machine and struggled through the crowded train to reach the guard to buy a ticket, as I was aware of the potentially serious consequences of not doing so
The consequences would have been a potential delay whilst you bought your ticket later on. But there was no obligation to do any of this.
In my view, penalty fare zones should only operate in areas where all the stations have ticket offices open at all times the stations are open and/or there are at least 2 ticket machines (in case one fails) at each station in the zone, otherwise the passenger (as in this case) is at significant risk of unfair prosecution.
I certainly don't disagree - personally, I think there should be much stronger enforcement of breaches of the Penalty Fares Regulations (by all parties, both passengers and TOCs), and a total abolition of private prosecutions - but unfortunately it would cost a lot more to fit proper facilities everywhere and it is therefore not in the TOCs' interests to do so, considering they have no obligation to fit multiple ticket machines and aren't paid any more if they do decide to do so. And as concerns private prosecutions, I can't see that happening in the foreseeable future as there is currently no major campaign I'm aware of.
Indeed the tinfoil hat wearing little part of me that believes the corporations are blood sucking entries draining the life out of the common man could easily believe the ticket machine being out of order is no accident of fate
As much as I'm up for pouring scorn on badly behaving TOCs, I really can't see this being the case. It's a case of inexcusable, almost criminal, incompetence and negligence on the part of the RPI and TIL. But there simply isn't enough cross-industry collaboration to engage in such collusion, to engage in any such collusion - you are expecting far too much from the competence of TOCs!
In short I don't believe that now it's the train company squeezing me for an administration charge, it's T.I.L. itself and my only hope of avoiding paying is to convince them they have no case. Which I suspect I won't be successful at to be honest
TIL are mere agents of the TOC, although they do act somewhat independently of the TOC in some regards. You are correct that one way of resolving the matter is to convince them to drop it. And that is certainly the easiest way. But if they persist, and the TOC is silly enough to pass it for prosecution, all is by no means lost. I would certainly advise you to obtain legal advice, initially by means of a (usually free) initial 30 minute consultation with a criminal defence solicitor. But that is for later, for a potential situation that may not even arise.