Again thanks OICURMT,
Your suggestion of changing mirrors allowed the upgrade to install a few differences in the sequence of install were required. I followed the instructions from
https://www.zdnet.com/article/how-to...6-04-to-18-04/
THet have a few extra steps to the list you provided.
They nearly worked on the first pass. At the end of the first run of
sudo apt dist-upgrade
I was prompted to try again with --fix-missing
that worked
The instructions that followed worked OK 18.04 was installed, It even preserved my desktop and screen manager...no Gnome,what a blessing.
Along the way I found that ubuntu 19 was available but not LTS. To download a non LTS version you have to edit
/etc/update-manager/release_upgrades and change the Prompt from LTS to normal.
I did not bother with 19.
If I feel brave after some testing I will update my work box.
An interesting journey
So many thanks
Chris