I'm asking this question as a result of an incident a couple of months ago, having just rediscovered the ticket in question whilst clearing out my ticket wallet. I sometimes buy a Cambridge to London day return + travelcard ticket for trips to London at weekends. I've always assumed that this allows a return journey between Cambridge and a London station (i.e. Kings Cross or Liverpool Street, or one of the stations on those lines), and then unlimited on the tube and National Rail services in the zones 1-6 area. First question - is that correct? On the day in question, I specifically wanted to travel to Liverpool Street, and then stay on the Eastern side of London (ultimately getting a SouthEastern service to from London Bridge to Charlton), so I opted for the cheaper version of the Cambridge to London ticket, that only allows travel to Liverpool Street, not Kings Cross. The ticket achieves this restriction with a "Route: NXEA trains only" addition - which makes sense, since NXEA don't run trains to Kings Cross. However, the ticket barriers to enter and exit the SouthEastern train service between London Bridge and Charlton didn't accept my ticket. I didn't really think anything of this (it's just one of those things that happens occasionally), and showed the ticket to the person manning the barrier, who always let me through without question. But thinking about this incident again has left me wondering whether the "NXEA trains only" restriction applies only to the Cambridge to London part of the ticket, or throughout the London travelcard area as well? And was I therefore allowed to do the journey I did on that ticket, or not? Experimenting with the East Coast journey planner, entering Cambridge to Charlton via Liverpool Street, I see that it doesn't offer me the cheaper "NXEA trains only" version of the travelcard. But it does if I enter a London Zone 6 station served by NXEA (specifically Harold Wood) - which adds to my suspicion that the restriction applies to the travelcard area as well, and I wasn't allowed to do what I did. If so, is it documented anywhere what exactly I can and can't do with this NXEA only travelcard? Tube? London Overground? DLR?