I think you're thinking of Homeplug type system which uses the house power wiring to network. When it works it's very convenient but success is subject to the wiring layout of the property. My own experience was a dismal failure with poor speeds even within the same room and lots of mains borne interference to audio equipment.
If you want to try this, arrange with the retailer that he'll give a refund if it doesn't work at your place.
thanks, do you have any idea what its called,
its going in an old converted police stationwith cells that are now flats. Or can you suggest any other way apart from the obvious, wired