Tubby and Two Sugars, thank you for explaining the intricacies of the 'Delta' and also some of the current frustrations.
I was one of the ~250 made redundant from BA in September 2020, being too junior to survive; I was booted out having aspired to join BA for over 10 years. Not being part of the company after that time, I'd only heard of the Delta from friends still at BA and no-one could tell me exactly what it was. Having read your explanations, I now understand (although I'm not sure it's legal). It's a further indictment on the continued broken relationship the management has with the pilot workforce.
Anyway, although I was 'happy' to be junior and bide my time, I won't be rejoining BA. Having seen it first hand and having used my time in the PRP to reflect on the realities of life at BA, I've decided it's not for me, especially over several decades of employment. I'm not bitter about it any more, I simply feel it's shame that what could be an amazing place to work, really isn't.