you really do need to detach the staff travel issue from the dispute itself.
If this was about hardship of individuals getting to work, I would have expected action immediately. I suspect that Unite
a) didn't consider that BA would follow through on the threat
b) expected this to be over by now and staff travel fully re-instated
You don't start legal action on the basis of the threat of removal and you don't start legal action if you are expecting the issue to be resolved within a reasonably short period. We now clearly have neither. Therefore legal action has been instigated because the premise of using perks as a weapon against individuals who have done nothing wrong, is in itself fundamentally wrong.
Removing all the political aspects to this issue of BA wouldn't want and Unite wouldn't want, looking at Unite's financial figures for 2009, I don't think you need to worry about whether they can afford this.