Maybe I'm not explaining myself clearly. The significant improvement was when I connected to the master socket and disconnected all internal wiring. However, I cannot live like this (with a cat5 cable coming out of the loft hatch and winding its way around the house), so had to reconnect the internal wiring, having split the wiring (which was star) into voice and data. The modem/router is currently on one section of internal wiring, so it will be worse for now, and I have to accept that. I will be returning to direct connection at the master socket when I have purchased, and had time to install, some external cat5 to route between attic and study, which are on opposite corners of the house.