Gentlemen,
You have a new name: ***** Superstar's *****.
Its was half a turn, clockwise!
I had previously tried to unscrew the two screws mentioned by Marc, but I was pushing against an end-stop. When I turned them half a turn clockwise (tightening), off the dial came. They are in fact the two blades that Geo mentioned.
I was beginning to lose faith, but now its onwards and upwards... until the next calamity :-).
Thanks again I'll post a pic when I put a new battery in the camera.
regards
George