Thank you, that worked! I opened the USB share to WAN and connected Beryl WAN to the BT Hub. The BT Hub assigned DHCP 192.168.1.175 and the USB share was available there. I set the BT Hub to always use that address, then connected the Beryl WAN to my 16-port switch and after first failing to connect, a quick power cycle on the switch fixed things and the USB share was available.
Just one slight issue remaining, I can’t get to the Web admin panel. Trying to browse from my PC to 192.168.1.175 gives “This site can’t be reached. 192.168.1.175 refused to connect. Try checking the connection. Try checking the proxy and the firewall”
Do I need to do something with port forwarding now?