Having checked the MB website, and the sequence of events following initiation of an ejection, It seems strange that Flt Lt Egging was found with his chute, yet the seat apparently was still in the plane / cockpit wreckage?
I seem to recall many years ago a Harrier(?) flying unmanned over the irish sea, apparently due to inadvertant firing of the drogue on the seat.
FT
A number of the events in the operation of MB Mk10 seats fitted to the Hawk are initiated by the seat moving out of the cockpit and not the pulling of the black and yellow handle. Two of them (firing of the drogue gun and initiation of the barostatic time release) will result in parachute deployment and aircrew/seat separation. (The other two are canopy MDC firing as the seat starts to move and initiation of the rocket motor as the seat fully exits the cockpit). Operation of the manual override handle will also fire the drogue gun and initiate parachute deployment along with aircrew/seat separation, though the Hawk may have an interlock to stop that from operating unless the B/Y handle is pulled. The Harrier accident in the late 1980s is covered
here