I recall Air 2000 using letter group MM with a callsign of JETSET. Memory hazy here but didn't Monarch use KG as their letter group? I don't recall ASCOT (RR) being used by other than Support Command. I'm pretty certain that the bombers shooting an ILS used their Mil callsigns; preceded with A/C Type if we were lucky. HSA Woodford flights always used the individual pilot's ident number; AVRO 1 being the Ch TP.