“Death of a Spy”, Scene 14: Inside the Horse

On these albums

Doctor Who: The Myth MakersDonald Cotton starring William Hartnell, Maureen O’Brien & Peter Purves · 2001Soundtrack

Doctor Who: Adventures in HistoryWilliam Hartnell, Patrick Troughton with linking narration by Peter Purves & Frazer Hines · 2003Soundtrack

Doctor Who: The Lost TV Episodes - Collection OneVarious Artists · 2010

Source: MusicBrainz recording 7c69eb63-8562-45ef-952a-9c1c57865ffc (CC0).