Just a musing...do any BA CC ever move between the three fleets out of LHR at present?

I know the idea is that, eventually, MF will be the only fleet, but if, for instance, WW saw a big slew of retirements, would crew in in EF/MF be given the opportunity to move between the fleets or even be seconnded?

Apologies if this has been asked and answered before.

Bobbie