Simon Heffer is the latest pedant (a self-description) who has a high opinion of his linguistic tastes and wishes "to inflict them on his readers". Everyone appreciates a good model, and we might expect the associate editor of the Daily Telegraph to provide one. But when I saw, reading the blurb, that "accuracy and clarity are within the grasp of anyone who is prepared to take the time to master a few simple rules", my hopes fell. The rules aren't few, nor are they simple. If they were, we wouldn't have books like this one.

The three main sections of Strictly English start with "The Rules", a 40-page summary of English grammar, spelling and punctuation. "Bad English" considers grammar, vocabulary, tone and three sinners (who don't use plain English). "Good English" summarises good style and explores three stylistic saints (George Orwell, Barbara Pym and Enoch Powell). Appendices describe correct address and points of house style and terminology.

The problem with people who want to impose their linguistic tastes on others is that they never do so consistently. Heffer writes that we "should avoid passives", but the opening sentence of that section begins: "The passive voice of a transitive verb is used . . ." Indeed, the book is full of passives, starting with the first sentence of his prelims. Don't do as I do; do as I say.

Heffer says we must avoid long sentences, but many of his own are over 60 words. Saint George's prose, he says, is "remarkably lacking in conjunctions precisely because his sentences are so short". But the Orwell passage he quotes has 11 conjunctions in 30 lines and an average sentence-length of 22 words. "Master of the short sentence" - not. Saint Enoch is worse, with some sentences running to over 80 words.

Inconsistencies permeate the book. Heffer doesn't like "task" as a verb, but he likes "text". Metaphor adds richness to language, but also dilutes the force of words. He prefers the "short word to the long", but berates Obama for using enormity instead of enormousness. The apostrophe "is never to be used to signify plurals" - but A's, B's and C's are a "sensible convention".

Heffer hides his tastes behind the idea of what is logical, using variants of the word more often than Spock. "Rules in language are made by logic, not by a democratic vote," he writes. If only that were true: it would save grammarians so much bother. In fact, there is no logic behind his recommendations, other than the usual kind favoured by pedants: if I like it, it's logical; if I don't, it isn't.

Heffer seems to be unaware that thousands study English language in schools these days. Writing them all off as "insensitive to language" won't endear him to their teachers, many of whom know more about grammar than he does, and would rather use the fine grammars written in the past 40 years than the century-old sources on which he relies. Maybe if he'd read some of the new studies he wouldn't have made so many errors in his presentation of grammar. He thinks that nouns can only be the subject or object of a sentence (they can also be complements and adverbial). And he says that a sentence has to "begin with a capital letter and end with a full stop" - dismissing all sentences ending in a question mark or an exclamation mark.

This isn't the place to mark Heffer's grammatical accuracy out of ten (about six, I'd say), but it's worth noting some examples of how we would all have to speak and write if we followed his tastes. We would be committed to saying "None of John, Mary or Jane was at the funeral", "queens mother" (for a lot of queen mothers) and throwing "a die" (not "a dice"). If we don't agree with all this, we are "semi-literate", "barbarous" and "illogical".

It is a pity, because there are some excellent points here about ambiguity, honesty and the importance of clarity. I'm as concerned as Heffer about the need to improve standards of literacy, but this isn't the way to go about it. He condemns the tabloid use of "shock horror" vocabulary, such as when someone is "devastated because his football team has lost a match". So what are we to make of someone who describes normal everyday English usages as "horrific", "butchery" and "abomination"? It's not logical, captain.

David Crystal's latest book is "Begat: the King James Bible and the English Language" (Oxford University Press, £14.99)

Strictly English: the Correct Way to Write . . . and Why it Matters
Simon Heffer
Random House, 352pp, £12.99