Though the other day I had a couple of these "Rail Enforcement Officer" bods walking up and down, but not checking tickets. I assume they're just there in a security capacity? Is this a new thing?
They're mainly there to deal with antisocial behaviour, crowd control, major disruptions and security, not check tickets. Apparently one of their accreditation bodies is not in favour of them doing regular ticket checks, as revenue is not their primary role, and if they have to deal with tickets/PFs, I believe they are not allowed to handle payments anyway.
However, if a passenger is found without a ticket and starts to "misbehave", or if there is a spate of regular faredodging, they are able to target appropriate areas and deal with specific offenders picked out by regular revenue staff.
Southern's RNOs (Rail Neighbourhood Officers) have been merged with the REO label, or at least in theory. As for how often they appear, they tend to pop up all over the place on the mainlines, but sadly there aren't that many of them. The Southern ones mainly deal with Southern-branded services and stations, and the TL ones tend to be found north of St Pancras, in my experience.
That said, I've seen a few more "Passenger Hosts" (ie. rebadged revenue staff) lately on trains south of the Core, which is good. And at all hours too...
