Without opening up old arguments
, there are a number of GSS Captains who are on secondment from BA mainline. In the past, BA Cargo was operated in house by normal BA crews. BA World Cargo has been at various stages operated by Atlas and now GSS. Atlas used 747-400s on the N reg with US pilots. After complaints to the CAA, it became GSS on the UK register with UK (EU) pilots. GSS continues to operate for BA World Cargo. A couple of years ago, BALPA negotiated for BA pilots to take command positions with GSS on GSS terms and conditions as GSS were doing entirely BAWC work and wouldn't be in business were it not for BA. Ideally, BA ought to be doing this work in house as before but the management are not receptive to this, hence the current situation.
If you do a bit of research on Prune, you'll find a few threads which delve into the politics of it.