Why are you assuming that the pilots in openskies are the enemy? Mainline has a scope clause, BALPA is the COMMON union and this is why they must work together. By taking this attitude now Carnage Matey you will alienate the Openskies pilots.
Of course the management are going to try and play one against the other, thats obvious, that is why BALPA must be one step ahead on this.
Incidentally, should BA attempt to break sched K (scope) then you WILL have the right to strike over broken agreements.