Look, as I say I am no expert, and my understanding may be wrong, but I believe it was started at around the time that DS and TW asked for the BA agreement to be put to cabin crew (the one that never was) and part of that agreement required Unite to agree to not take legal action against BA with regard to staff travel and disciplinaries.
So I believe that some crew were upset by this and set up Crew Defence but as I said I am not completely sure of my facts, so please do not assume I have got all the facts completely right.
These are my views and they may be completely wrong and they are definitely not those of my employer BA.