If you have it on an extension sometimes trying it on the master socket with the extensions disconnected (on most master sockets you can take the front faceplate off which will disconnect any extension wiring then expose a test socket you can plug into) if you get faster speed at this point its your extesion wiring.
Of course it could just be the Homehub although they are a nice idea and the features they offer are quite good (wireless,dect basestation, voip.etc) their build quality is somewhat lacking IMO.
you could either try and persuade BT your Homehub is faulty and get them to send you another one or you can use your own modem/router.
My homehub was DOA and since i don't like them anyway i use my own ADSL router with my broadband
