The MYSTERIOUS CIRCUMSTANCES title was used to group a series of 26 half-hour radio plays distributed by the BBC Transcription Service. The thrillers were either recorded for BBC Transcription Services or taken by them from the BBC's main archive -- some may never have even been broadcast within the UK itself. I've uploaded the 18 I have -- unfortunately many are in poor sound quality but a few are very good.
Episodes run from 1958 to 1989 and perhaps beyond.
- The New Catacomb [by Sir Arthur Conan Doyle] (4.5Mb)
- A Glass of Lemonade [by Barry Bermange] (7.8Mb)
- What Do You Think? [by Francis Durbridge] (unknown file size)
- The Goblins Who Stole A Sexton (Sir Ralph Richardson) [by Charles Dickens] (37.2Mb)
- The Demon King (by J B Priestley) (27.1Mb)
- The Dancing Partner (by Jerome K Jerome) (38.7Mb)
- The Lady on the Grey [by John Collier] (7.6Mb)
- An Unrecorded Instance [by Marie Belloc Lowndes] (11Mb)
- Martin's Close [by M R James] (31.5Mb)
- W.S. [by L P Hartley] (unknown file size)
- Night Drive To Dover [by Julian Symons] (4.5Mb)
- Oh Whistle and I'll Come to You [by M R James] (32.6Mb)
- Returned Without Thanks [by Berkely Mather] (4.6Mb)
- Markheim (by Robert Louis Stevenson) (26.5Mb)
- Cold Storage (by Philip Levene) (39Mb)
- The Drowned Village [by Berlie Doherty] (24.2Mb)
- The Secret Sharer [by Joseph Conrad] (11.7Mb)
- Fiddler of the Reels [by Thomas Hardy] (7.7Mb)
- Markheim [by Robert Louis Stevenson] (7.7Mb)
- Shadow of a Magnitude [by Michael Robson] (4.3Mb)
- The Monkey's Paw [by W W Jacobs] (4.5Mb)
MP3 files hosted by archive.org.