This wasn't during a strike but to cope with day to day disruption. With poor training. On your days off. I did say not as cabin crew. Managers in BA aren't what you would expect in other industries but includes people who do not manage people at all. Making them managers means you don't have to pay them overtime and can tell them to volunteer!
What makes you think this is peculiar to BA ? It is quite normal for managers to be salaried, and thus expected to work overtime for no extra renumeration. It is whats expected in return for the enhamced salary and benefits.