Unfortunately, it's not 'TOTAL nonsense'. Please see Corbyn v Saunders [1978] 1 WLR 400, in which the Court found that there had been an opportunity to pay and that he did not take that opportunity: "when passing the ticket collector at his final destination, the requisite intention to avoid payment is proved" and that this judgement is used daily in prosecuting RoRA S.5 offences where 'any' opportunity to pay is not taken, not just 'an' opportunity.
Unfortunately, the 'several' who think that najab is 'clearly wrong' appear to be similarly unfamiliar with the jurisprudence of railway law.
Having said that, I agree with ainsworth74 that " the layout of this event is so crucial." and "If in the passengers line of sight was a ticket office and the revenue protection staff then I would say that approaching them to buy a ticket is unlikely to allow a TOC prosecutor to show intent to avoid a fare." It is 'unlikely', but not impossible, and certainly not 'TOTAL nonsense'.