LW (EGLL) Tower Supervisor
LW has a pretty good memory for these types of things; I'll ask him when I next visit him!! (son of LW). I believe he used to give a 30 second warning to the 2nd halves on a night shift in the Tower by starting an irritating whistle before he scaled the Tower stairs. Gave them a chance to clear away all the flotsam and jetsam before he huffed/puffed his way to the Sup's position.