Train Strikes September 1st

[worsy]

I need to be in London Friday and booked my ticket some months ago. I understand that I am able to travel on that ticket the day before or up to Sept 5th (I think).

Part of my journey is on Transport for Wales who are not striking on Friday. Does anyone know if I will have to buy a ticket for Thursday to travel on TFW or if all train operators acknowledge the rules (so to speak) ?