GWYN,
Haven't got a set of Jepps at hand, but, am fairly sure that JAR states that first contact with tower,gnd,approach should include the preamble " heavy " . It is of course for heavy wake turb a/c not just cat. D a/c, eg; 767-2 cat C but HEAVY.
I have always thought this was just a belts and braces thing for a busy ATC enviroment at first contact, and helps other drivers who of course haven't got your flight plan with their situational awareness.
BB