This is a potential mine field and at best (me being a union person), it will be seen as unlawful. If it goes BA's way, then it could seriously damage collective action in the UK, even more so than this current dispute has.
If you are correct Litebulbs that this dispute will have far-reaching negative implications for future Union action, it is even more depressing that this dispute arose over a few hundred CSD's (many of whom were BASSA reps) being told to push a trolley.