A few points about the 1997 dispute. Bob Ayling was a lawyer, so would have had a reasonable view of the legal ins and outs. The points laid out then were a combination of direct possibilities (dismissal for breach of contract, liability for damages) consequential actions (removal of staff travel) plus punitive measures (no promotion, removed from any options for early retirement or severance available under various re-structuring schemes).
BA has had two changes in CEO since Ayling, neither of whom have opted to resurrect the global tailfins, so it is not guaranteed that when the current incumbent said that staff travel would be withdrawn, it mean that it would be returned with full seniority. The point I'm making is just because one CEO acts in a particular way is no guarantee that others will follow suit. Moreover, my understanding is that previously staff travel was not universally withdrawn, but only applied to those who went on strike.
If the unions had considered BA's actions to be aimed at preventing staff from exercising their right to strike, why did they not pursue this in 1997 ? There has been no change in the TULRCA.