Hmm, I used to work for BT Openzone, and I never heard of two Hubs being applied like that. I think it would be improbable as they work off different WEP keys etc, but it might be worth calling them up to check. Don't worry, BT Openzone / BT Fon are UK based, heh.
I think a booster would be the best way to go, from what I've heard, the plug-in ones aren't too shabby. The best way to use them in an old thick-walled house would be to position them as near enough "line of sight" of each other as possible. So if the hub is in the next room to the computer, put a booster out in the hall between the two so that the signal gets "bounced" at a right angle to the computer.