The Union rules state that if the govt announces a sale of the rest of it's shareholding (or part of) then the union shall ballot for industrial action. It's there in the standing orders, there's no way round it (unless members vote to give it up). Each member needs to let their rep know what they want to happen should the govt push the plan further, rather than bleating about what has gone before and fighting amongst ourselves.
Not quite true, Section A3 3.1 (xii) of the Branch handbook stated that "The BEC shall ballot members for industrial action should the Government announce that it is to sell off its remaining stake in NATS".
However, Motion 5 at Conference 2009 "Conference instructs the BEC to lobby Department of Treansport and Industry to allocate a portion of any future sale of shares by H M Govt for the exclusive purchase by NATS staff.", was passed and the procedural attached to this motion was the deletion of A3 3.1 (xii).
So it appears there is no such manadate.