One time my ticket was on BA I think and the last leg was actually a AA flight from Miami to Tampa. I was flying through LHR. I hadn't yet got a boarding pass for the last leg, when I arrived at LHR there was two ticket counters as I left the plane, one was BA and the other AA. I could touch the counter for BA and AA at the same time. They both told me the other one was responsible for giving me the boarding pass. At one point I had to say to both of them at the same time, very loudly, one of you needs to give me a boarding pass. Then they started arguing with each other, that's right, the BA counter was arguing with the AA counter. Finally one of them, I don't remember which side, handed me a boarding pass, finally. I would say this system doesn't work.