Hi there,
The only way to connect the BT hub to another router is via cable. There is no wireless bridge available.
There's a couple of things to do to get the BT router to work as an access point and if you follow some best practices it should work without a problem.
The router that is doing DHCP needs a narrower scope, say 10 - 254.
Change the IP of the BT router to something outwith this scope, anything from 2-10
Disable DHCP on the BT router. And that's it.
Thanks