Some good news and some bad news. Finally back in the land of home and I have the RJ45 connection working - BUT the speed is poor. I guess that is the result of using untwisted wires.
Thanks to all for the help in trying this, and I'll leave the swanky RJ45/BT plate on the wall. My laptop is giving me a 5 bar wifi signal while the desktop alongside is showing only 2, so I guess the next step is to buy an extension aerial for the desktop to improve the speed, since the dinky little aerial on the PCI card is right at the base of the rear of the PC.
A useful exercise for me, anyway, in 'education'
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