I’ve just watched the Channel 4 “Docu-drama” (still available on 4OD) about the activities of the little known MI19 at Trent Park House. It was decided that the house be used for higher ranking German prisoners of war, however there was a lot of preparatory work done there before the first inmates arrived. Two other houses were also given the same treatment ready for other German PoWs. MI19 laid what was probably miles of cables and installed microphones in every room, they even installed microphones in the trees in the grounds. The intention was that given the right conditions of comfort and presumed security the German generals held there would start talking amongst themselves … and they did. Apparently the general idea was to acquire some understanding of the Nazi mindset which could then be fed into other surveillance material obtained through other intelligence gathering methods. One of the “big” secrets was the confirmation of the intelligence about the V2 facility at Peenemunde already noted by the Photograph Interpretation Unit at RAF Medmenham, codenamed “Operation Crossbow” which led to the massive raid by RAF Bomber Command and resulting in the facility being moved east, well out of range of the RAF and the rocket programme being put back by six months or so. Some of the other secrets divulged by “careless talk” was regarding the mass murder of Jews in Russia and later in France. All the conversations between the inmates were recorded, translated and transcribed, the intention was that they should be used at any impending war crimes trials, but in the end, none of the inmates were accused of war crimes and under orders from Churchill the recordings were destroyed before the could be used and the transcripts locked away in the National Archive. Churchill was by then becoming aware of the threat posed by Stalin and Communist Russia, later to be known as the USSR and he didn’t want to reveal how the British Intelligence services came by such insights, thinking that the techniques might be of use at some later date. The transcripts apparently came to light in the early 2000’s quite by accident after a historian asked for some papers about German U-Boat activities and he was given some of the Trent Park transcripts by mistake. Just another set of “secrets” which although no longer locked, they're just lost in the dust on some shelf somewhere in the National Archives at Kew.