"The inspector probably also noted the ticket details, so they will simply ask Trainline for the buyer's details. Email addresses are regarded as personal data, but the app will know some more than this. They can share the information because GDPR allows sharing data where necessary for vital interests like fraud prevention, but also app users will have agreed that personal details may be shared for combatting crime, which GDPR calls consent."
Sorry but you're just making that up. Please show me where there is a "vital interests" clause in the GDPR. Please also show me the app user agreement that says that a person's details can be "shared for combatting crime". So if I buy a train ticket for the 13:30 from Kings Cross and someone is assaulted around that time, then my details can be shared to "combat crime", because I must have been on the station at the time in question, and it could have been me?
That is absolute nonsense. I set out above the circumstances when GDPR allowed information to be shared, and as I said it cannot be shared for the purposes of a fishing expedition, which is exactly what it would be, because the railway company think that the alleged offender is Bloggs, because Smith gave them Bloggs' details, and when they are shown that it isn't Bloggs, then they have to go fishing around to try to find out who the offender might have been, and as I have said repeatedly now, where does that get them anyway? It simply shows on whose app the ticket was purchased. It doesn't show who purchased the ticket or more importantly who travelled on the train, and who used the ticket.
There might be a dead person on the ground and I might be holding a knife, but you still have to prove that it was me that killed the person on the ground, and that I intended to do it.
The railway company should have asked for proof of identity of the person in possession of the ticket at the time, and recorded that information. Since they didn't do that, there is a fatal flaw in their case.
They have to prove their case. They have to prove beyond reasonable doubt, i.e. so that the Court is sure that Smith was in possession of the ticket and using it illegally and they cannot do that, because short of an admission now from Smith, they cannot prove that.