Replying to my own post here.
I think I have made progress. By chance whilst talking to our IT Manager we looked at the test site in the server room to see the problem and something I had dismissed as a local/network caching issue cropped up (see attached images one from chrome and one from IE) and we were able to say that it had just been fetched from the moodle server.
So in fact it looks like the files are corrupt.
I have to say it is the first time I can ever remember being really pleased to have discovered that data has been corrupted.
I know we have a clean version of the data on the external hosted site but what I would like to try and establish is if the dvd that we were sent with the database and other files on it is good or corrupt.
To this end is there an easy way to fish a file from the file store on this disk?
I am thinking of doing a file search with a very constrained file size filter to match a file I know is corrupt.
Any better ideas.
Thanks again for all the help.
John.