The law says who must? BALPA are not the employer. BALPA may suggest but they cannot compel. If BMI merged the list with BMed it's because BMI felt they had to. A union cannot force an employer to do something against their will. The law says sweet FA about pilots seniority lists. BA employ lots of people doing the same jobs on different contracts. BA can legally run the BMI pilots on a seperate, standalone fleet, with different T&Cs and no access to the master seniority list or the Postings and Promotions process and be fully compliant with TUPE. Once you understand that you are half way to recognising the reality. It matters not what BALPA say. All that matters is what IAG/BA can do.