Anyway, many thanks to Mike Easter (Apologies for the vague specification of my system), Jonathan Little and Henry Crun. I followed Henry's instructions to the letter and it all worked very well.
One peculiarity of my system is that there is no eth0 but there is a enp4s0 instead. I think this was at the root of my problems in trying to follow instructions on the net.
Just two remaining problems.
1) I don't seem to be able to restart network-manager.service but this doesn't affect my ability to access the network so it is of low priority.
2) Unconnected to networking. Why has Pan changed the pane layout and provided no means to recover that I can see?
Best Regards and thanks again, Jack Fearnley