to Cable Forum. I've moved your post to a separate thread since BT's FTTC and Virgin Media Cable are two different systems and thus your situation could have different issues.
Firstly with regard to your choice of Draytek Dual Wan router, do check the various specifications. Some are designed to handle more connections / throughput / bandwidth than others, so make sure you opt for once suited to your LAN network needs.
Some Draytek routers have an ADSL modem inbuilt. If they do you probably do not need the Vigor 120. Some routers do not have an integral ADSL modem, thus you may need the Vigor 120.
The BE ADSL service can probably be run using the BE supplied modem / router (from which you would connect it's LAN port to the Draytek WAN 1 or 2 port), or via your own supplied modem i.e. the Draytek router - or 120.
The FTTC service probably has to use the FTTC service's supplied router, but again you should be able to connect the LAN port of that to a WAN port on the Draytek, in much the same as the VM Cable superhub LAN port is connected (at least in my office) to the Draytek.
You may need to check with BT / Be as to how your incoming telecoms services would arrive at your property. I suspect you would have two distinct phone services, one with the bundled FTTC line, and a completely separate service with the Be ADSL. I doubt they can both run over one incoming wire, indeed there would be little point in that since the one wire would be a common point of failure. Most dual broadband services are done for redundancy, rather than speed.