Get the Devolo box that plugs into the router and sends an ampilfied signal around the wiring in the walls. Maplins have them.
How does the signal leave the wiring - does the kit come with a re-broadcaster to put in specific rooms?
You've got these, which are excellent and hardwire your home through the power circuit: http://www.amazon.co.uk/TP-Link-TL-PA211KIT-200Mbps-Powerline-Ethernet/dp/B004INVKP4/ref=sr_1_1?ie=UTF8&qid=1341925523&sr=8-1
Or this: http://www.amazon.co.uk/TL-WPA281-Powerline-Extender-Wireless-Access/dp/B0067GS0YO/ref=pd_sim_computers_3