I dont have access to it anymore but JSP 356, has a list of ranks for all three services and it used to have the EMR's (Equivalent Military Rank) for civilians...
eg....
An AO would be equiv to F/L
Professor would obviously be higher up the food chain...probably in region of Harry Staish or 1 Star area....
Rarely do you see PC Plod saluting Sir Chief Constabule on his rounds...in fact dont think i ever have....