Our understanding at present, is that your basic pay can only be deducted for the time during which you were participating in industrial action, although we haven't, as yet, heard back from our lawyers - we will however publish our legal advice in full tomorrow, for your guidance.
I would be very wary of advice from BASSA's lawyers. They (as with BALPA's lawyers over Openskies) don't have a great track record against BA's lawyers.