You could start by looking at your hub manager -Advanced Settings-My Network. Find your BT box in the list (if it's ever been connected since you reset the hub, it will still be registered) and check if the background colour for that entry is Green (connected) or Grey (not currently connected).
Make a note of the IP address and scan and up and down the list to make sure there are no duplicates. Exit the hub manager.
Go to settings on the TV box and set it to use a static IP address, enter the address you noted earlier. The box will automatically do a connection test, if it fails then the likelihood is that the box is faulty.
Many thanks for your reply. I’ve looked at the settings and can’t see any entries for the BT box. I’ve sorted by IP address and can’t see any conflicts. Everything was working fine a couple of days ago. Is there anything else you can suggest?
This smacks a bit of desperation but it's all I've got I'm afraid.
When you reset your hub, it would have restarted with Smart Setup enabled, you could try disabling it.
Even more desperate, move the network cable going to the TV box to a different port on the hub.
Edit: you're not using power line converters or wifi extenders etc are you?