It beggars belief today, but Gyles Brandreth comes from a near-mythical time when a media-friendly MP could also be an intelligent and literate person with a broad cultural hinterland. Now the colourfully sweatered stalwart of Countdown and organiser of the first British Scrabble championships has bounded ebulliently into the rich market for books about how to write proper. Naturally, I took up my mechanical pencil and prepared to festoon the margins with proofreading marks.

I was in for a pleasant surprise. It is almost an iron law that writers who tell other people how to write, from Lynne Truss to Simon Heffer, will as often as not get things technically wrong and break their own rules. It happens only very rarely here: I counted a couple of mis-identified Americanisms and two unfortunate dangling participles. “First seen in print in 1494, the playwright Ben Jonson was the first English writer of significance to use [the colon] consistently,” he says, implying that Jonson started writing 78 years before he was born.

Many competent writers can do everything Brandreth recommends in the book, but would be hard pressed to enunciate the rules in a clear and entertaining fashion. This is where Brandreth excels: he is brilliant, for instance, on the difference between the semicolon and the colon. “Look at the colon and think of it as a pair of binoculars placed vertically on the table,” he advises. “It is there to help you look ahead.” He is sound, too, on dashes and apostrophes; on the difference between “may” and “might”; on how to form unusual plurals (“lord lieutenants”, “attorneys general”). I was especially pleased to see him insisting that you need a comma “to separate two independent clauses when they are linked by a coordinating conjunction” (like “and” or “but”), since one person who used to have the misfortune to edit my writing systematically removed all the ones I put in, which was a dagger to my tiny heart every time.

The book is also very funny, and often outright silly. He insists that beginning a letter “Hi, Gyles”, with a comma between salutation and name, is “sinister”, and translates the phrase “Your call is important to us” quite directly as “Fuck off”. Naturally, he enjoys a bit of name-dropping (the Queen’s “comfort breaks” during official duties, he reveals, are scheduled with the marvellous euphemism “opportunity to tidy”), and entertaining anecdotage: “I was invited to host the British Funeral Directors’ Awards and found that the main prize of the night was for ‘thinking outside the box’.” Anyone who uses the word “whilst”, meanwhile, he insists is “subliterate”.

Some readers might not have predicted that a former Conservative MP would be so liberal and happy about modern changes in usage. He counsels his audience to read “the rappers” as well as Jane Austen, and enjoys the possibilities of expression represented by new terms for sexual orientation, or online initialisms such as FML and YMMV. Even with a usage he personally finds irritating, such as “bored of” (rather than “bored with”), he consults “my friends at the Oxford University Press”, who tell him it is now very common. Only occasionally does he put a fogeyish foot down, insisting that “Can I get?” (the coffee-shop version of “Can I have?”) is “wrong, wrong, WRONG”. It’s hard to see why, since no misunderstanding is possible, and I suspect that “Can I get?” might even be an adorably polite display of diffidence, an unwillingness to focus on my own greedy desire to have something.

It’s a shame, though, that Brandreth also feels he needs to pay lip service to the idea of “political correctness” as some kind of dark language-inhibiting force, perhaps because the market for such books skews to an older demographic. “You can have lots of fun with political correctness,” he says brightly, before hoping to demonstrate his point by making up a list of things that literally no one has ever said, eg: “Don’t call them ‘dead’ – say ‘they’re metabolically challenged’.” But it’s clear his heart is not really in it, because elsewhere he writes: “The Brandreth Rule is simple: at all times avoid racist, sexist, homophobic, and transphobic language – and, when in doubt, err on the side of sensitivity. In my book, bigoted language, and language that can be perceived as bigoted, is bad language [...] Good communication is about courtesy and kindness as well as clarity and getting your message across.”

Of course, such basic decency and consideration for others’ feelings is all “political correctness” really means. So he is, happily, on the side of the angels, in all his linguistic joie de vivre and amusing self-awareness. Indeed, if this Brandreth Rule were not more honoured in the breach than the observance, the world today would be a much better place.

• Have You Eaten Grandma?: Or, the Life-Saving Importance of Correct Punctuation, Grammar, and Good English is published by Michael Joseph. To order a copy for £8.59 (RRP £9.99) go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99.