Is it possible to connect my FVS336Gv1 through VirginMedia Superhub?

Until Sunday I had a simple setup of LAN to WAN using Virgin Media Business 50Mb service. GS724TP managed switch connected to FVS336Gv1 firewall/router connected to VirginMedia Business (VMB) cable modem/router to the outside world. It all worked beautifully but on Sunday the cable modem just died. VMB responded quickly and provided me with a new cable modem on Sunday, but since then I can't see the Internet through my existing LAN configuration.

I can't understand why the existing LAN configuration won't work when only the cable modem router was replaced and it was a straight model swap. Has anyone else come across this problem?

When I contacted VMB for tech support, they told me it's not possible to connect a router to a router and I'd need to purchase 6 static IP addresses to make it work????? Until Sunday, I had only 1 static IP address configured on the cable modem router and it worked fine.

Do I need to bridge the routers to get through from the LAN to WAN to Internet?
Do I need to have DHCP switched on on both FVS336gv1 and the cable modem/router? I've tried switching each one off alternately, but no joy. They are connected from the WAN1 port of the FVS336Gv1 to the 1st ethernet port on the cable modem. The GS724TP is connected from a vacant port to an ethernet port on the FVS336gv1. Could it be any simpler?

The domestic version of the VM superhub allows the router part to be switched off, to use it just as a modem, but the VMB version doesn't have this option (at least it's not shown).

I've reset all of the Netgear kit back to factory settings to try with a clean "out of the box" configuration but still the magical connection eludes me.

Any ideas gratefully accepted.