We have discussed Beaker Street Theater in passing. (Dale, correct me if I have any of this wrong). For the most part, the "theater" radio dramas came from George J. Jennings' collection of old time radio shows. These were also used on the morning drive time program and were known as "Breakfast Serial". George took thirty minute or hour broadcasts and cut them down into short episodes. For Beaker Theater I believe he used mostly BBC or South Africa programs to give them a more modern sound and programs that were not familiar to the American audience. It also made Beaker Theater different from Breakfast Serial.
I do have some of the original reel to reel tapes If anyone in interested, email me at firstname.lastname@example.org.