@woozle Yes, I have changed the cables and moved devices and the problem still persists in the same location. I am thinking of the possibility of some kind of noise or interference on the mains...

@stevei Hi woozle Thanks for the reply. I have 4 devices, 3 in use. I have swapped them all around and it makes no difference.

My powerline setup has developed a very strange fault. By a process of elimination, I have found that one of my devices shows about 200 mbps when nothing is plugged into the ethernet port. However,...