Who or What was ENSOC?

This is a photo of the Hotspur MkIII rear fuselage before it was restored and used in the replica at the Museum of Army Flying. The airframe has obviously been used as a decoration at some event – hence the strange paint job, markings and trimmed down fin.
So who, what and where ENSOC?
The fuselage also had two different serials on it HH379 with BT860 beneath. As far as I can find out BT860 outlived HH379 but obviously after a change or rear fuselage (wsa it removed for repair or modification?