I Just Want To Fly,
I think it works differently if you are to be based at a different base as opposed to just flying from it. I flew from STN, EDI and NCE on my LGW pass, but would always return to my home base afterwards.
EZY did introduce their own ID not long after I left. It could be a case of just having it validated by the ID unit at the base you transfer to, but I stand to be corrected of course.