See this link
There are other alternatives on this page.
That link is for the home hub 3a as main, I have to 2 home hub 3b's.
You can try them, but you may find problems if you roam from one home hub to another, as the HH3b did have a software bug, which may have been fixed now.
The other alternative would be to use the BT wifi extender.
If you can connect your devices using an Ethernet cable, then a BT Broadband extender should work, as they use the mains wiring.