Litebulbs,
no matter what historic agreements BA had with bassa about what its reps could and couldn't do, and how they were paid whilst "on TU duties" BA will have a rock solid case for the ending of all the facilities. Whilst I've never worked for BA, I suspect that there will be a set of entirely plausible actions and decisons based not on BA's behaviour, but on bassa's behaviour.
For instance, once bassa said that it would not negotiate with BA, and passed that resolution at a Branch meeting, BA would be fully entitled to both close the reps office, (and all its facilities) and to re-scedule all of the reps to work, (rather than be permanently removed from work schedules).
Thus, there is no potential finding by an ET that DH was employed as "a rep" when he refused to attend work. BA's paperwork will be robust on this subject.
............and if it isn't, I suspect they will not care.
Don't forget, ET's cannot substitute their judgement for that of the employer. All the employer needs to do is to argue that their actions were within the range of reasonable responses that any employer might have.