I do not know of any off airport lighting as such other than red lights on masts but LHR used to have an enormous flashing green beacon on the South Side of the airport which kept going long after VHR ATC and radar were the norm. Also, the famous Gasometers (themselves a thing of the past) north of LHR which sometimes confused crews whether they were heading for LHR or Northolt and the one for Northolt had the dual purpose NO in huge letters on the top.
So I am not surprised that pre war high locations on an approach path to Croyden or later Northolt (Harrow on the Hill is close by) might have had some kind of beacon on them given that visibility around London in the days of smog wasnt that great at times