Thanks for the help, but it's not working still - it does (sometimes) work if I move the router around downstairs, but due to the location of the superhub restricting where I can situate the router I can't leave it where I get a signal.
So I've bought these, and hope 30 quid is going to be worth it just to stop me throwing the PC through the window:
http://www.ebuyer.com/263575-tp-link...roduct-reviews
Thanks again, Mark