I missed this earlier... Ray it could well have been a talented soldier rather than a war artist. There were some seriously skilled folks out there. One of my former neighbours (no longer with us sadly) was one of Monty's tank crew and he had sketchbooks from his time in the army (and from before the war as a "cub" on a local newspaper in Radcliffe.) Wrong initials for him but my guess is someone like him. It's very well-done for sure.
Probably the best way to try and find out would be to see if there's a veterans' group for Monty's men and ask if they have a newsletter in which they would put out a note asking for info, or archives that might have other examples of the same person's work.