More frustration and not resolved. I spent a fair bit of time on the phone with the Draytek support people. They walked me through setting up "Router policies" so that any traffic being directed to any specific website (or IP) was instructed to bypass the VPN.
I set it up, so that it the router was instructed to bypass either the website (e.g. bbc.co.uk) or the BBC's IP address (151.101.64.81) and all traffic to either of these should pass through WAN1, and not the VPN. It didn't work - as the Humax Freesat box simply won't play content through the BBC iPlayer app.
The error code on the screen: The link is currently not available. [Ok].
Any other thoughts by any chance? Interestingly, the NOWTV streaming boxes connect and work just fine - and these are also using apps from the broadcasters. They're slow to load and navigate around, but they work.