Will post back after son looks at system.
Meanwhile, have tested using extra long ethernet cable to link hub in one room and PC in second room and this shows that BT speed test to hub is 75 and 2 other speed tests also show speed at PC as 75-78. So definitely wireless problem in hub. Problem not caused by wireless distance from hub to PC as I have tested with wireless tablet beside hub and through beside PC and both show BT speed as 76 and other speed tests as 45 - 50.
Tried all of the suggestions, wifi analyser showed good channel was being used, but nothing made a difference. Consistently getting reading of 20 higher using ethernet cable as compared to wireless.
Previous set up was - livingroom - BT phone socket with master cordless phone and hub connected, TV connected to hub by BT wifi extenders plugs. Bedroom - desktop PC and cordless extension phone.
Moved hub to bedroom and set up hub to phone extension socket (not previously in use), ethernet cable from hub to PC and wifi extender plug to second ethernet socket on hub. Left master cordless phone in livingroom connected to BT phone socket.
Seemed to work well with increased speed to PC and TV in livingroom still receiving wifi, although had to reboot TV box. However, then found loud hissing noise when using phone in either room.
Have finally set up - livingroom - TV still connected by wifi extender, phone using cordless handset not connected to BT socket. Bedroom hub and master cordless phone connected to extension phone socket, ethernet cable to PC.
Works well, but now have hub and master phone (with answering machine) in bedroom. Not best choice, but does increase computer speed. So will go with that. Ideal solution would have been to move computer to livingroom, but just no convenient location there. Note: problem is not wireless distance of PC from hub, even in same room speed is much lower on wireless compared to ethernet, which is the same as BT speed test shows hub receiving.
Sorry if this rambles, but I'm trying to explain in full.