The pilots of both companies know that if they are run as seperate opco's then they will be played against each other.
eg. BMI becomes BA Express - then after 6 months IAG offer them a 25% pay cut.
They can't strike because BA mainline will cover their operation!! Or vice versa. Or IAG will simply let IB Express do BMI's work.
BMI guys are
if they don't join BA.
BA guys could vote no, but then all new work would go to BA Express (on their very lean T's and C's).