It’s very common for people to assume there is a “correct” variety of English that follows grammatical rules, whereas informal speech relaxes those rules. In effect, we can let our hair down when we’re among friends and not worry too much about the rules of grammar.
This is all wrong. Whether we use formal or informal registers, we always follow complex grammatical rules. This is true of standard English and also non-standard dialects, which follow slightly different rules. For example, many non-standard dialects allow multiple negation — You ain’t seen nothin’ yet — whereas standard English doesn’t.
This is where tags come in. Tags are short interrogatives that come after an affirmative or negative declarative clause. There are lots of tag questions in English, aren’t there? You do understand this, don’t you? I’ve made this clear, haven’t I? Tags are characteristic of speech, where we generally want confirmation that the person we’re talking to has understood and is following the conversation (and they’ll usually give a nod of assent as a response). They’re also used in relatively informal edited prose. …a newspaper columnist will generally adopt a conversational style rather than a formal register.
While being informal, tag questions exhibit complex grammar. I haven’t remotely got space to give a comprehensive account of these rules, but here are one or two characteristics of tags. A tag has the same auxiliary verb as the one in the declarative clause. The subject is a personal pronoun orthere. It involves subject-auxiliary inversion (isn’t it, not it isn’t). And in the most common form of short interrogative, there is what linguists call reverse polarity. That means negation of a modal or auxiliary verb, or removal of the negation if it’s already negative. (There is a less common construction that uses constant polarity, but it generally implies irony or indignation: “So you’re a world authority on grammar, are you?”)
Moreover, there are irregular structures in the grammar of interrogative tags. You can’t say amn’t I: it’s got to be aren’t I. However, you can’t say I aren’t, or indeed I amn’t: it must be I am not. If you’re a native English speaker, you will automatically follow these grammatical rules. And if, like many Times readers, you’re a fluent non-native speaker, you’ll have had to painstakingly learn them.
Now, while English has many possible tags, there is one that’s quite recent in the language. It’s innit. Having originated in London, it’s become widespread in speech among young people. Formally innit is a reduction of isn’t it but it doesn’t strictly mean that, as it’s also used as a replacement for any tag question, negative or positive, and with verbs other than be.
Do you hate innit? That’s OK; it’s not part of standard English and there’s no need to use it. It follows grammatical rules too, though. As a tag that’s invariant to tense and semantically empty, it’s analogous to n’est-ce pas in French, which is a standard construction. Perhaps in another 50 years Times and Sunday Times columnists will be writing innit and no one will bat an eyelid. Rest easy: English will survive just fine.