At the risk of repeating oneself.
1) I think that the members of the union/s should be more proactive and insistent in their demands to their representatives as in my opinion you are being lead by the nose too easily.
2) If you genuinely believe that there is/are potential safety issues or violations inform the Civil Aviation Authority either individually or collectively.
3) If number 2 is valid perhaps you should approach BALPA for a meeting as the pilots and passengers are the ones who will pay.
4) Raise your concerns with your management and keep the written records of the meeting.
I think that if you fulfil your moral and legal obligations by drawing attention to these deficiencies and still nothing is done then I think you would be justified in involving the press (Look what it has done for the MPs integrity)
I think that in the event of an accident you would a) have a clear conscience
and b) nats spokesmen mouthing "Our thoughts and prayers are with the families" and "Lessons will be learned" will not wash.