We know that the CIA takes writing seriously. Magnificent euphemisms such as "enhanced interrogation techniques", "extraordinary rendition" or "illegal combatants" were clearly carved with care out of the language.

Few people imagined quite how seriously, though, until last week, when the Style Manual and Writers Guide for Intelligence Publications (Eighth Edition, 2011) began to be disseminated online. The book, which is 185 pages long, offers comprehensive instruction on the writing of "clear, concise" spy reports – in much the same way that newspaper style guides advise subeditors and writers. As director of intelligence Fran Moore writes in the foreword: "The information CIA gathers and the analysis it produces mean little if we cannot convey them effectively." (Note the singularity of "CIA", and its lack of a definite article.)

And what sticklers her agents are! Operatives are reminded that "disinterested" means impartial, while "uninterested" means not caring. There are wise warnings about the dangers of a dangling participle. ("After being waterboarded, Agent B found that the subject became more loquacious." My example.)

At first glance, however, the directorate of intelligence clearly sits closer to the conservative end of grammatical opinion. They stand by the Oxford comma, for one thing. And while liberals might consider the battle over "hopefully" lost, the book insists that it still means "with hope" and tells operatives to "avoid using the word in the sense of it is to be hoped". To use split infinitives, which many writers now consider as optional as a fourth sleeve button, the CIA requires full justification. "Make sure that clarity or the flow of the sentence demands the split," the book says. "If you are not sure, do not split."

CIA style is also tinged, perhaps appropriately, with patriotism. British spellings must be Americanised even when they occur in a proper noun. Thus the CIA would only talk about the "Labor Party", should they ever have anything to say about them. In fact they don't like foreign words generally, outside those deemed "sufficiently common or functional" to be included on a list in chapter eight.

And in places you can almost hear the power rushing to the authors' heads. In the "Word Watchers List" at the end, there is mention of an elite squad within the directorate – the "redundancy police", whose list of banned phrases evinces an unmistakable love of power. Sure "first began" and "sum total" are best avoided, and "adequate enough" is plainly awful. But surely there are contexts where one would be justified in specifying a "young baby" or allowing the emphasis in "build a new house" when an old one stood there before? "Peevologist" is the name often given to people who enjoy this kind of petty and often faulty fault-finding. (Kingsley Amis preferred "wanker".) In this context it marks just the sort of drift into authoritarianism that Edward Snowden warned about.

And do they even put their sermons into practice? On Monday the official CIA twitter feed said "We flew an A-12 OXCART, not a SR-71 BLACKBIRD." Yet, as page 59 explains, that should have been "an SR-71 BLACKBIRD". Someone will be "reassigned" for this.