[SunTzuWu]

Fast-food chains including Domino’s Pizza, Pizza Hut, KFC, ­Nando’s and Subway are also using halal meat without ­telling customers, it was revealed

I don't believe that for even a minute.
1 - Halal meat has to be more expensive that the usual variety because it is a low volume specialty. No business is going to voluntarily cost themselves more money.
2 - Compared to modern slaughter houses, halal slaughtering can't supply the volume of meat needed to keep these listed restaurants in product.
3 - This story is from England and the places named are in England. I don't think you have any need to boycott your local Domino's or KFC.

[Pan_Yans Wife]

A KFC in Marietta, Georgia serves halal meat.