Human Factor
HMRC did have a go at ST some years ago. They proposed to tax the fare at the full price value of class travelled, as a ''benefit in kind''.
After some time the proposal was dropped, but not before threats by crew not to carry Govt Ministers etc etc!!, probably not workable.
The fact that ST was not contractual only a 'perk', counted heavily in our favour of HMRC not proceeding at that time.
If BASSA win a case, using the contractual argument, this could mean a huge tax implication for all staff.