But to answer the question, when I started at Heathrow in the late-60s, the ICAO code for the Vanguard was VC9 (with the Viscounts being VC7 and VC8 and the VC10s and Super VC10s, VC10 and VC15 respectively). That later changed - in the early 80s if I recall - to VANG (including the Merchantman), VISC (all models) and VC10 (all models).
Pete, thanks - that's just what I was looking for!
When I was a First Officer on them we had to file flight plans (later it was automatic). When filing a plan while away on a night stop, we all three crew went to the department in the tower and the junior First Officer filled out the form...I the day I am thinking of, the junior man was me. I just could NOT remember the Captain's name and I remember dawdling my input onto the form while struggling to remember his name before I got to that particular box (Captain's Name). Anyway, I finally got there and had a bright idea..."How do you spell your name sir?" I asked briskly and looking all innocent...