The Queen's English is correct, conventional, standard British English. It is the most authoritative and easily understood form of the language. One finds it in non-fiction and fiction, in textbooks in almost all subjects, in newspapers, in government and business documents, and in public and private correspondence.

Departures from the Queen's English do get noticed. The head of an online graduate recruitment agency wrote that they reject one third of all job applications from graduates with good degrees from good universities, because errors in English in their CVs and covering letters show ignorance, carelessness and a bad attitude.

The term "the Queen's English" dates back to 1592, Queen Elizabeth I's time, but using the Queen's English is not the prerogative of royalty or any class, group, region or country. The Oxford English Dictionary defines it as: "the English language as regarded as under the guardianship of the Queen; hence, standard or correct English".

Without accepted rules and conventions, and agreement on the meanings of words, there would be linguistic anarchy and lack of understanding. The standard form of a language is the one which all people should be able to use and understand, wherever they come from, although they may prefer local variants for local communication, such as regional and ethnic versions.

The Queen's English, with correct grammar and vocabulary, can be spoken in many accents, say Indian or Australian, and in regional British accents such as those used in Birmingham, Newcastle or Glasgow. There are extremely good users of the Queen's English in Sweden, Sri Lanka and Singapore, and very bad users of it in London, Oxford and Cambridge. There is much ignorance, carelessness, inverted snobbery and deliberate "dumbing down", as if bad English is more socially acceptable than good English.

Standard English should be used when writing business letters, essays, reports, job applications and on all formal occasions. Most people here use it automatically nearly all the time, without consciously thinking: "I am using the Queen's English."

Other forms of English are completely acceptable in appropriate situations. For example, in plays or films involving characters with strong regional or ethnic dialects, the author would not write standard English for them. A problem with non-standard English is that it can cause confusions. For example, in Malaysia, to have an "off day" means to have a day off, not a bad day, and to "chop" a document means to rubber-stamp it, not to cut it. In Britain, one finds people using "sick" or "wicked" to mean good, with great scope for misunderstandings.

Deviations from the Queen's English include errors in grammar, spelling, punctuation and word choice. I heard a man on a train say: "Me and him gets on great". The two pronouns should be in the subject case, not the object case; the verb should be plural as there are two subjects, and "great" is an adjective, when an adverb is required. One should put oneself last, so the correct version would be: "He and I get on well."

One can have a sentence that is grammatically correct, but ambiguous, such as: "This room needs cleaning badly" or "Mary told Jane that she was pregnant." The former would be clearer as, "This room badly needs cleaning," because word order affects meaning. In the latter, the pronoun "she" could apply to either woman.

The world of advertising often uses corrupted English, as in the slogans "Beanz Meanz Heinz" and "Drinka pinta milka day". Odd spellings are used, such as "lite" and "nite", perhaps to catch the eye by being unconventional. These should be avoided.

It is repeatedly said that English is a living, changing language. We do need new terms for technology or new phenomena, and English has such a large vocabulary because it has absorbed words from many languages.

The Queen's English is not fossilised and takes in new words, phrases and usages, but it should not embrace usages which blur meanings. For example, we have clear distinctions in meaning between to effect/to affect, disinterested/uninterested, imply/infer, their/there/they're, defuse/diffuse, complimentary/complementary, fewer/less. We lose precision and clarity if we lose those distinctions, and confusions of such words are extremely widespread.

New phrases may be worth adopting if they convey a meaning that is neat, clear and concise – such as "yummy mummy".

It is sometimes argued that grammatical rules are invalid because some great writer broke one. That is nonsense. Great writers understand the rules and can knowledgeably break them occasionally for specific effects such as surprise or humour.

The Queen's English observes the distinction between proper nouns, with initial capital letters, and common nouns. A journalist correctly described Richard Branson's daughter as "Holly Branson, the Virgin heiress". "The virgin heiress" would have had quite a different meaning.

Correct punctuation is needed to convey clear meanings. Far too many people fail to use the apostrophe correctly, if they use it at all, and are poor at using semicolons and colons. When marking undergraduate work, I rarely saw a correctly punctuated piece by a home student. Public documents now are often littered with errors in punctuation and grammar, as well as spelling. A female tax officer wrote to me about my "penison" – a Freudian slip?

"The Queen's English" is sometimes used of speech, meaning the same as "received pronunciation", "Oxford English" or "BBC English" (as it used to be, but often is no longer). For general use the Queen's English pronunciation is best, as it is the clearest and most widely understood kind. I have sometimes found myself unable to understand announcements, at stations or on trains, because the announcer had a strong accent. Announcements may be important for safety as well as for catching a train, and should be understandable by all.

In 2006, CoPilot Live mobile phone satellite navigation published the results of their survey in different parts of Britain as to what type of spoken English people there wanted to hear as the voice on their sat-nav devices. The Queen's English was the overwhelming favourite in all parts of the country, from Birmingham to Newcastle, and even in Northern Ireland, Scotland and Wales. Regional accents can be enjoyable and can help to give a local sense of identity, but for understandability at national and international levels, standard Queen's English is best.

Some of the finest spoken English today can be heard from the morning newsreaders on BBC Radio 3, with beautiful clarity. Compare that with speakers elsewhere who have "gonna-rrhoea" ("I'm gonna play you..."), word misuse and glottal stops ("I was li'erally gu'-ed when I missed that penalty t'night"), or wrong grammar and missed word endings ("Me an' Jim is runnin' late..."). I know which I prefer: the Queen's English, in speech and writing. Why settle for less?