The rules cited come from the essay Politics and the English Language. [i] The style guide of the Economist newspaper is predicated on that essay. [ii]

[i] https://www.orwell.ru/library/essays/politics/english/e_poli...

[ii] A copy of The Economist style guide at archive.org - https://archive.org/details/EconomistBooksTheEconomistStyleG...

- the latest edition is sold via The Economist and by some book sellers.