If you are using Devolo power line adaptors to extend your IP network to your BT box, there's a good chance that the October firmware upgrade broke multicast/IGMP and stopped the UHD channel working. If your adaptors haven't yet updated to 5.6.1 then I suggest that you turn off automatic updates. If you have already upgraded, and your UHD channel doesn't work, then get in touch with the Devolo support team. They were brilliant, and remotely downgraded my adaptors, which now works fine again (FW 5.3.4).
Many thanks Devolo!