Thanks skappy, but I've tried all those things!
Tried different sockets, cables, ports, different distances to hub, turning off everything but hub/YouView/TV etc. - none of it seems to make a difference!
I received my BT youview box yesterday and finally set it up today. I kept getting the same issue (IPC6023) for a few of the channels such as History channel, Fox, Sysfy etc.
I'm not using the BT Home Hub as I sent it back to BT, i'm using a Netgear Nighthawk R7000 router instead. I came across this article: https://community.netgear.com/t5/Nighthawk-WiFi-Routers/R7000-cant-get-to-work-with-iptv/td-p/513192... mentions "Most IPTV providers use IP Multicast but most firmware for consumer routers have little to no support for IP Multicast".
It mentioned for the Nighthawk R7000 that "Disable IGMP Proxying" needs to be deselected so i accessed my router property page and downloaded the latest firmware update for my router and then disabled IGMP Proxying and now i can view the channels that I was only getting IPC6023 before.
I'm not sure how much this helps as I guess you must be using a different router but hopefully this will point you in the right direction.
I just noticed that StephanieG has put up instructions on how to enable multi casting for a number of routers.