If BA can make redundancies currently in its Cityflyer subsidiary I doubt that there will be much legally stopping them doing the same to mainline. The best the staff might get is that the threat of legal action, even if rather futile in the end, may make the company improve the redundancy terms. I dont see any airline coming out of this crisis with the same amount of staffing as they went in with - there are going to be many colleagues out of work for a long time.