Yep, using one right now in my parents room. Ours is the BT Smart Hub 1, we got it just before their change of policy and needing to return it.
1. Find the Mac address of your BT Smart Hub.
2. Go to your Router (not the Smart Hub) and get to it's Static IP settings. Make sure the Smart Hub is always given 192.168.1.254 (It's default access IP) or to whatever IP you want to give it.
3. Plug in the Smart Hub if not powered up already. Connect to the Router via ethernet to one of the NORMAL RJ45 ports at the back, not the VOIP or the WAN port, one of the normal ones.
4. Set up the Access Point details on the Smart Hub as you want it to (access default IP via browser).
And that should be that.