Leenig

The quickest way is to go the BT site and Opt out

This will take a few hours to work it's way through the system. If it doesn't show you opted in. opt in wait 24 hours than opt out this should then remove the BTFON from your home hub. You must leave the home hub connected whilst you do this otherwise it will not change the settings on it.

Could it be that you originally opted out when the Home hub was not being used?

In reply to a post by MHC:

If someone want to run a Gbit network then choose a decent switch to do it, don't rely on the router even if it has four Gbit ports. Modem to interface to the line, router to manage the routing and a switch to handle the traffic. Minimise the load on individual parts where possible and let them do what they are designed to do.

Only one reason for a single gigabit port (as Draytek 2820 has) is for the WiFi - N can often run faster than 100megabit.

Wired LAN to N WiFi - and forget the WAN

For one device maybe ...

And only if it is within a metre of two!