I'm using a Vigor2927ac in my home/office connected to two broadband connections (WAN1 virgin cable + WAN2 Cellular 5G modem), almost everything works as expected.

The only issue is that our Virgin TV on-demand service only works on the Virgin Cable broadband, so it only works reliably if the 5G connection is unplugged from the router.

Is it possible to have the Virgin TV box (currently plugged into its own port on the Vigor router) always use WAN1 while maintaining the load-balancing / fault tolerance for the rest of the network? If so what's the appropriate way to achieve this?

Any help would be appreciated.

If you can give the Virgin box a fixed IP address can't you then use load balancing/route policy to force it to use WAN1?

Yes, that's done the trick, thank you.