Just arrived from pub therefore slightly cerebrally challenged.
Are GSS F/Os BALPA members?
Try to get BA crew onside - i.e. don't alienate them.
Make it a 'BA vs crew' issue rather than a 'GSS F/O vs BA F/O' issue.
Looking at it from the outside you have points on both sides AND (unlike Cathay's probs over the last 10 yrs) you are in Europe with UK/EU labour laws and union representation.
Look at the law - e.g. why can't BA sub their freight if they wish?
GSS FOs - where does it say that your company can't employ DE captains? Did you have a promised command clause in your contract? (most 'promised commands' don't)
BA FOs - do you wish to help create a B-scale cargo subsidiary?
Please don't consider any of the foregoing to be adverse criticism; merely food for thought based on a few years in the biz.
I'm going to see what's on the tele