Hi Dave, thanks for the response. See info below-
TV and Hub have both been rebooted. I've been using an Ethernet cable to connect the TV to the Hub, don't think this is faulty as the TV sees other settings on the Hub, but not the IP or Gateway addresses(?).
Time and date are both correct on the TV. TV has not ever shown that an update is required or available.
The Hub settings do not show the TV is connected- perhaps this is a clue?
I've now switched the TV to wireless mode and can now see YouTube again, but I suspect the reported fault is still there. I'll try a new Ethernet cable tonight and see if that fixes the fault....