I will be very interested to see the wording of the ballot paper as this will be the key. Certainly from what a couple of posters have said, it may not dot the legal "i" or cross the legal "t", which means it's consultative only.
If it is consultative, there cannot legally be a strike at the end of it, which means it amounts to rabble rousing and that is likely to cause BASSA/Unite to be held liable for any costs incurred by BA. Pointless in other words.