To go along the "'Officially' striking for just one day may actually be interpreted by BA as several days unavailable for work, depending on when an individual striker actually next turned up for duty!" line, how would it sit if someone "pulled a sickie" or refused to show because their roster had them on longhaul before/after the strike date. So one day would be "striking", when they would not be working, but since they would be in, say, Hong Kong on the strike date with no way of getting back home, etc, they took a day or three "off" unofficially, due to the timing of the strike, then surely the result would be that it is "interpreted by BA as several days unavailable for work" and disciplinary action could legally be taken as appropriate....
Litebulbs, it's over to you.