I have the username and password - I know these work for the standard set up.

Unfortunately, the "Business" Hub 5 just has Bridge Mode = Yes/No and no settings. Yes disables DHCP, routing etc.

I have tried all the various settings in Multi-PVC on the Draytek though not all VPI/VCI settings (I have tried 0/30 and 1/101).

i think it does not need any settings at pcv, for just setting the HB & use the 2820 as simple router only
just settings at wan>general setup & wan> internet access for setting the wan 2 to work with the HB

Having spoken to BT, they said that bridge mode does not work on the BH5 out of the box despite being in the UI but it (currently at least) needs a firmware update. Crossed fingers for that.

They also confirmed there will be no more VDSL modems available and bridge mode on the BH5 is all they will support for use with 3rd party routers.

well i don't know if my suggestion will help you because the method below can not use port forward if you need due to double NAT
So just in case if you don't need this feature, until they will update the HB can use the HB only for modem by changing its IP address (if is the same as the vigor) disable wifi,dhcp for not any coflict
here how option 2,
http://www.forum.draytek.co.uk/viewtopic.php?f=2&t=19712#p81508

In the BH5, I think it might be possible in your second option to set up static routes that route all traffic to the draytek and set up the reverse on the Draytek. However, I have no wish to go down that road as it will be horrible forever.

BT updated my firmware from 4.7.5.1.83.8.198 to 4.7.5.1.83.8.200 and PPPoE worked first time once I switched bridging mdoe on again. Thanks for your suggestions!