Ok. I take it all back. Arthur C Clarke probably didn’t steal the idea of ancient astronauts meddling with humanity and civilization from Nigel Kneale. There’s at least a 4 year gap between Encounter and The Pit. I think it’s probably a case of unconscious cross fertilization. They were both original, ground breaking writers who didn’t need to plagiarize.

https://en.wikipedia.org/wiki/Encounter_in_the_Dawn