As I said, some of it is "officially" written down in an unsigned newspaper letter to the editor.

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

Notably the article doesn't even know if the letter is still the law or not.

> Following passage of the Dissolution and Calling of Parliament Act 2022, which repealed the Fixed-term Parliaments Act, these principles are thought to have been revived.