Big Tudor
As you say, BALPA sought legal advice regarding the issue of sexual discrimination; however it would be discrimination against the male pilot if a lower service female was kept over the longer serving male pilot. I believe it's to do with actual compensation. It would be cheaper to compensate the male pilot than the female pilot so I was told by BALPA.
LIFO is great and fair for redundancies and it would be also fare if it meant LIFO based on date of promotion, but not on date of joining as it has been agreed between BALPA and the company.
I personally will be stopping my subscription from the union.