Far, far easier said than done. How do you establish what station he got on at? If there’s CCTV on the train, then you’re contacting the train company who won’t want to spend very long reviewing footage from every carriage he’s been into for an unknown period of time to establish where he got on.

Then you’d have to review CCTV at the station to establish the exact time he’s tapped in or bought a ticket. Then, contact whatever merchant sold the ticket - that’s it you can tell without contacting the operator, because obviously you’ve got third-party ticket retailers like Trainline.

While you’re doing these enquiries, bear in mind the radio will constantly be going off with jobs to attend over the multiple shifts it’d take – all with investigations to pick up from them. BTP travel a lot too – they’d always be 45 minutes away, so they’ve got very little time to process things.

If you’ve got payment details, you’re then dealing with a big financial institution who may or may not be helpful. The only way to force them to provide details is a production order – which needs a magistrate to sign off on. It’d take hours to get that hearing organised, and it might not even be possible to get one – because unless an injury has been sustained this could be the summary only (‘not serious’) offence of battery.

You might have traced a suspect if the same person paid for the ticket. Organise an interview. If they don’t turn up, travel hours to their house to arrest them. Maybe they don’t admit it in interview to deal with them out of court – so it’s going to be a charge and spend hours building the file of evidence.

All to get a £50 fine at court.

And maybe you can cut some of that down by using facial recognition… only if the footage is good enough and their custody image is held on the national database – which means they’d need a previous conviction.

In short, TV makes it look easy. It probably took me as long typing that as you’d think it’d take to identify a suspect!