Stupid loving AMC made some stuffty cunt agreement with BT, and gave them exclusive rights to show Fear The Walking Dead.
BT has their own AMC/BT channel, where AMC provides all the content (none, besides FTWD, Breaking Bad and Mad Men (both of which showed when they were actually airing on Sky Atlantic), and then just American movies).
You can't use the AMC/BT channel (even though it's available on Sky), unless you purchase a subscription to BT Sports.
It's really loving stupid.
Fox has the rights to broadcast The Walking Dead in the UK, so it makes no sense at all why they wouldn't try to get the rights to show FTWD.
As a result I've only seen the first episode, when the channel was made free to view, and to be honest, it was pretty lackluster.
At least The Walking Dead starts up in a week. (Sunday 11th for US, Monday 12th for UK).