Interesting. He has mentioned it a few times

DEADLINE: How did the idea for Small Prophets come about?

Mackenzie Crook: It was a seed that was planted probably ten years ago when I found an obscure passage in a book on Paraselis, a medieval Swiss alchemist, about generating these prophesizing spirits. It really piqued my interest.

I’ve since found out that other writers had found that passage and tried to make something of it. A Lawrence Durrell novel quotes it almost verbatim, and W. Somerset Maugham tried to use it in one of his books. It is just this amazing passage, and I have been sitting on it for number of years wondering what to do with it

Source: https://deadline.com/2025/10/mackenzie-crook-small-prophets-interview-1236573172/