BOAC
The IPA were approached, by ex VA Company Council members (VACC), but for reasons I cannot recall they did not proceed. Their conclusion was that it was better to start afresh with a brand new union as they had lost faith in BALPA as well. The debacle of the lost strike was handled in an appalling fashion by both BALPA HQ and the VACC.
There is far more to this story so I will give you the brief version. What happened next was that VA pilots were awarded the very same pay increase that had been unacceptable only months before. To understand why there was so much anger directed at BALPA you have to understand that 97% of the pilots voted in favour of industrial action. The BALPA General Secretary decided, for reasons best known to himself, to call off the strike. Some, possibly many, of these pilots will have come to the conclusion that BALPA HQ had an agenda other than protecting the interests of its VA members. At the very least it was staggering incompetence on the part of the union to advocate a course of action that it was not going to follow through on. It is worth considering that every other airline board of management now knows BALPA is all bluster.
The founding directors of the PPU are mostly ex VACC members who were committed BALPA members and who defended the pilots' interests in a tenacious and intelligent manner. They did not desert BALPA, it left them.