It was indeed RWR, fitted to RAF & RN birds from '74. Think the last one to be fitted (to operational a/c - BAe & Mod test ships didnt get'em) was 1986.
Aah, having re-read victor twos post I believe you are referring to the ILS aerial, again fitted to RAF only birds from '75??
I know its not a photo forum but do you want more pix??