In the mid 80s ,I believe some of the instructors from the college of ATC,either in their spare time,or perhaps following retirement used to do some training leading to TWR/APP licence & ratings.Maybe this was the 'back of a Volvo' scheme alluded to in post#2.At least one of the RAF controllers I knew at Eastern Radar obtained his CAA licence this way. Think he went on to work at Warton.