Partially solved problem...
This is very complicated.
Firstly you need to download regionset
Then you need to find where your DVD player is on the system.
In my case it was /dev/disk/by-id/[name of dvd player]
That path will be different for individual systems.
Then you need to sudo regionset [path to dvd player]
If the region code is set wrong, you can select Y to change and then put the correct region code for the disk you want to play. Note that the DVD player region code can only be changed a limited number of times, then it becomes locked and you have to replace the entire drive if you move to a new region.
After performing the above steps the media players no longer delivered the error messages, and attempted to play the content. However.... the content does not play well, it is distorted. A very disappointing result, however it is worth noting that this was in fact the solution to the actual problem of not being able to play the disk, Now I have to work out how to fix the playback so it looks right. That's a new task!