Here is what I think you are asking: You have a BT Home Hub with Wireless that is working. You have a Belkin wireless router that you would like to use to get wireless coverage in part of your domicile where service from the Home Hub is not functional because of attenuation due to construction materials, namely lots of rock. You would like to locate the Belkin on the other side of the lots of rock to serve that area. Is this correct ?
Can you get an ethernet cable from the Home Hub location to the proposed Belkin location ? This is a key bit of info as it influences the path forward.
Assuming that the cable mentioned above exists (big assumption), what you want to do in semi-techie terms (in case you need to refer to it later) is convert your Belkin from a Router to a Dumb Access Point.
Here is the easiest way to do that I know of. Since I don't know the model of your Belkin the steps will be somewhat generic, you may have to look up the exact how-tos in the manual (gasp!) or online. This process is similar for most home WiFi routers. Please read all the way through this before you start, and if anything isn't clear ask first.
Be aware oddness may occur until you complete the setup. Don't try this while your significant other is attempting to watch their favorite show or movie on Netflix or their Roku.
Connect to your Home Hub network, wired or wireless, from your PC or Lappy. You need to figure out what address you have been assigned by DHCP (automatic address assignment) on the Home Hub. If you are on Windows you need to get to a command screen (Start->Run->cmd or similar depending on version) and in the DOS-ish looking window enter "ipconfig /all". You are looking for two things, you IPv4 address and your Default Gateway. They should be located about 20 lines down from the top and MIGHT look like 192.168.1.<something> and 192.168.1.1 or 192.168.1.254 respectively. Write them down.
Now we need to make a "hole" in your network addresses for the Belkin to live in. The problem is that the Home Hub probably assigns DHCP addresses across the entire range of available addresses, and we may get a collision if we assign the Belkin an address that is already, or will ever be, assigned by DHCP. Since you probably don't have 253 computers on your home net at any one time we can narrow the range a bit to make room for a few statically assigned addresses.
Follow this handy guide to get into the Home Hub LAN settings menu:
The process is a little different depending on the version of Home Hub you have. Also these instructions leave out one very important step, but we'll get to that in a moment.
You will need to disable the DHCP server per the instructions for your box, save changes.
Now change the DHCP address range to something manageable (I use 192.168.1.100 to 192.168.1.199 for my home network, for example).
Write down the range you use. Don't change anything else. Save changes.
Now the important but left-out step from the instructions above, re-check (or un-check depending on your version) the box you checked (or unchecked) to disable the DHCP server. To be clear, we want the DHCP server on the Home Hub box to be ON. If you don't do this everything in your house that gets an address automatically will quit working at some point over the next few days. That can be annoying.
OK, we should be done with the Home Hub.
We need a PC or Laptop with an Ethernet cable to set up your Belkin. If it also has WiFi please turn that OFF. We really only want to talk to the Belkin over an Ethernet cable.
Plug in your Belkin and connect to it (one of the 4 "local" Ethernet ports) from your PC or Lappy with an Ethernet cable. Don't connect the Belkin to anything else except power. Your computer should be set to get an IP address automatically. Give the Belkin time to boot up then try to connect to it. By default it should be at 192.168.2.1 (web browser http://192.168.2.1) and a the password prompt leave it blank. If it's changed you may have to go find your IP info as above, the router should be at the Default Gateway address. If the password is changed and you don't know what it is you may have to reset the router to defaults. This usually involves "The Paperclip Of Doom" and a small hole in the back of the router, hold down the button for a few seconds until the lights (on the router, not the house) blink. After a power cycle and suitable boot-up time the defaults should work again.
Once you are in the router we need to go to the WIRELESS settings. We want to set the network name (SSID) to the same thing used on your Home Hub WiFi, with the same passphrase and security model (usually WPA2). This will not let you roam seamlessly between them, but it will let you connect to whichever is strongest wherever you happen to be when you connect. If you move around you may well lose and re-establish your connections, so watching movies on your tablet while jogging around the house is not advised. Locate and change the network name (SSID). Locate and change the Passphrase (often under a "Security" button. Save the configuration (will probably cause router to reboot.)
Log in again if needed.
Once you are back in the router we need to go to the LAN settings. Again, the exact steps depend on the model of router, but you should be able to follow along. We need to change the LAN address to something that matches your Home Hub network, but not something used by the existing modem/router or any other device. Find the LAN address (should be 192.168.2.1 if default) and change it to the gateway address you wrote down for the Home Hub network but with the last digit of 2 (if your gateway address ended in .1) or 253 (if your gateway address ended in .254). Write this address on a sticky note or strip of tape and stick it on the bottom of the Belkin. Don't save yet as it may be difficult at this point to get back into the router.
While we are at it we want to disable the DHCP server on the Belkin. This is usually under a LAN tab. You may have to hunt a little but it's there. It may be called DHCP or "Assign Addresses Automatically" and may be under an "Advanced Settings" tab. Once it's turned off you can save and reboot.
At this point you probably cannot log back into the Belkin - that's fine as we've pretty well told it to shut up and go away, which is what we want.
On the back of the Belkin there are 5 Ethernet ports. 4 are in a group and one is all by itself. Find some tape and stick it over the one connector that's all by itself. Some little note that says to avoid connecting to that plug helps. Now connect the Ethernet to the Home Hub to one of the other 4 ports. Reboot your PC or Laptop while it is connected to another of the 4 ports on the Belkin and when it comes up you should have Internet access (and if you check, probably the same IP address you had way up at the top when we started, and more importantly, the Gateway should be the address of the Home Hub). If that works you can disconnect your PC/Laptop Ethernet cable and turn on your WiFI again. If all is well you should connect to WiFI with a nicely strong signal and be able to access the Internet.
TaDa! You just made a Belkin into a dumb access point and 4 port switch. The DHCP and routing for the entire house is now handled by the Home Hub. You've got a few extra Ethernet ports in Belkin land in case you need them.
If you are missing the Ethernet cable between the Home Hub and Belkin locations you might want to look at Broadband over Powerline as a way to interconnect them, or even use one of the Broadband over Powerline WIFI extenders - they pretty much do what we just did above but without the wire and without the extra Ethernet ports on the Belkin end.
Good Luck !