if flying out of one uk airport and into another uk airport via Dublin, at what point do they claim that’s a domestic flight and therefore cabotage provisions apply? Does cabotage even come into the CTA? What about doing the same from ?LBA-AMS-SOU

i’d like to believe that even if cabotage rules are going to be thing in this situation, LCY-DUB-LHR would essentially be treated as a simple return, due to both UK airports being LON. But would that be the case? And what about examples via other ports as above?