Last Tuesday (11th August) I took the 1155 LNER from York to Dundee, no onboard checks whatsoever, and while the barriers were staffed at Dundee, passengers were summoned through an open gate with no requirement to produce a ticket.
Foregoing the option of a rail replacement bus, I took a Scotrail (1033) from Dundee to Edinburgh yesterday (19th August). This time gates were open at Dundee, with no staff in the vicinity. No on-board ticket check, but the train terminated at Platform 15 at Waverley, and the gates were closed - so a valid ticket was required to exit the "terminus platform" area. (Side note - this was a "Fife Stopper" and became - at least in the current climate - fairly busy, with no reservations on board, and passengers boarding at later stops were sharing both Airline and Table seats with some who were already on board).
Finally, I joined with the 1230 Edinburgh service to Kings Cross, leaving the train at York. Again no on-board ticket check, or indeed any requirement to present my ticket for this journey on either station. There were one or two people on this train who kept being "evicted" from seats by other passengers who had reservations for them. I'm not implying those being moved didn't have a valid ticket, but merely a reserved seat, so if mandatory reservations are required, then they do really need to be policed to be effective. (Sorry, that last bit was slightly "off-topic").