Might be 198.168.0.100 if the Virgin box is in modem mode in order to pass traffic through to the Homehub.
If the homehub and Virgin boxes are connected to the same LAN you may have the problem that both will be trying to use 192.168.0.1 and the BT may have won. Try switching of the BT and using a PC that is connected with a network cable to the Virgin box.
Would help to know what is the response from the addresses you try?
If using Windows, double-click the Network icon. You may see a device calling itself 'ARRIS TG2492LG-85 Router'. If so that's the Virgin router and you can double click on that to launch the admin.