Fast Track at T2 is the right of main security. It's essentially Star Gold fast track, and that's what the agents are looking for overwhelmingly, though EI status holders can use it. But BA status holders do not have status on Aer Lingus (or any non oneworld airline) and so Fast Track and Priority Boarding doesn't work there. There is lounge benefit on Aer Lingus, for unrelated reasons and is a bit of anomaly to the basic line that status doesn't transfer outside oneworld.