It can be quite interesting reading agreements (though I guess BA has so many, covering different work groups it would not be a good idea to publish them for all to see).
(We have one agreement covering all staff (there used to be three) that is freely available on the company intranet)
You find that if the company and the lay reps can't reach agreement, full time officers automatically get involved.
You find that the company is there to manage the business, the unions to intervene on behalf on the employees
Obviously in this case there are 2 separate branches of the same union involved it would, possibly, make sense for the full time officers to be negotiating.