Staff travel is at the sole discretion of BA. It can be withdrawn at any time. You have no recourse.
How do I know this? It has happened to BA retired staff. Not withdrawn in its entirety but gone from 'in perpetuity' to '= length of service'.
I understand that a few staff have ST as a contractual right and that they are mostly in IT. I could be wrong there but that was the rumour. It was also rumoured that some IT staff have an enhanced DoJ for ST.