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On 4月20日, the following important behind-the-scenes events were known to have occurred:
- 1964 - BBC2, the United Kingdom's third TV network, was launched. Henceforth, the main BBC network, which aired Doctor Who, would be known as BBC1.
- 1967 - Location filming The Evil of the Daleks began at Grim's Dyke House. (TCH 10)
- 1971 - Location filming for The Dæmons took place. (REF: Doctor Who The Handbook: The Third Doctor)
- 1980 - Studio filming for The Leisure Hive took place at BBC Television Centre studio 3. (REF: Doctor Who The Handbook: The Fourth Doctor)
- 1987 - Studio filming for Time and the Rani took place at BBC Television Centre Studio 8. (Doctor Who The Handbook: The Seventh Doctor)
- 1989 - Location filming for The Curse of Fenric took place. (Doctor Who The Handbook: The Seventh Doctor)
- 2002 - The Big Finish audio story The Rapture took place at the Moat Studios.
- 2004 - The Big Finish audio story The Juggernauts was recorded at the Moat Studios.
- 2010 - Big Finish's Bernice Summerfield audio story Escaping the Future was recorded.
- 2011 - Big Finish's audio adaptation of the unproduced TV story Meltdown (retitled Power Play) was recorded at the Moat Studios.
- 2015 - The Big Finish audiobooks The Shadows of Serenity and Prime Winner were recorded at the Moat Studios.
- 2016 - The Big Finish audiobook The Hesitation Deviation was recorded at the Moat Studios.
- 2018 - Recording for Shellshock took place at Audio Sorcery.