@ Airclues
That's interesting. However, I really don't believe that there could be any challenge to further IA based on it requiring a longer notice period (I think this is what you suggested?). I am pretty sure that many interpretations of the act (including that published in the Department for Employment and Learning's pamphlet ER29 'Industrial action and the law: A guide for employers') make it reasonably clear that during discontinuous IA, the dates can be changed as long as 7 days notice are given.
However, where there may be some sort of legal challenge possible is if BA believe that "the result of a ballot no longer represents the views of union members or that something has happened or is likely to happen which is likely to result in union members voting against taking, or continuing with, action if there were a fresh ballot".