Further enquiries revealed that the image was made up of 4 normal resolution images meaning the image had more potential than first anticipated:-
The photoshop automated photostitch option gave ghastly results as below:-
So I decided that to get a printable quality these would have to be joined together "manually". This involves many layers of work with the images aligning, erasing, cloning, changing lightness/contrast, distorting etc etc. Much of this can be avoided by using the same exposure for all images.