As a BA shareholder, it is very much "my" business.
"As a BA shareholder it is very much [your] business" to interest yourself in the running of that company - to a certain degree, that is true, but after that you leave the day to day management of BA in the hands of its chairman, directors and the leadership team appointed by the BA board.
"As a BA shareholder" it is absolutely none of your business to poke your nose into the internal affairs of a trade union you do not belong to, have not belonged to and etc etc etc.
By your logic, because you may pay council tax in a town "it is very much [your] business" to investigate what that town's employees wear, eat for lunch and so forth.
Let BASSA members challenge their branch secretary to produce audited accounts; it is absolutely no business of anyone else - not even the self-appointed inquisitors of the PPRuNe SLF threads.
And for the avoidance of any possible doubt, and before the herd instinct kicks in with snide negative personal comments against me, I am not nor have I ever been a member of any trade union during the course of my entire life.