Zippy's words:
still hold a letter of intent to that effect from easyJet, offering me - subject to satisfactorily completing the six months - an offer of employment.
No mention of temporary, probationary perhaps, but not temporary, and his experience of BALPA support does not in any way validate your statement.
the primary function of a union is to protect members' T&Cs
On the evidence in front of us we can comment and deduce that support is not universal.