Madbob
I have already replied to you in length but it must have gone astray. Sorry, but I was a tutor at E.F.S, the old Empire Central Flying School which became E.F.S. when the "C" became the Central Flying School at Little Rissington.The E.F.S was a sort of University type of establishment for high ranking Officers and civilians of many countries. Your relatives were at the Empire Test Pilots School , E.T.P.S a sister school and much sought after course as it was a "must" for any would be Test Pilot.
Good luck in your search. By the way, I have wondered where that light went for a long time but never thought of hiding it there. Regle