A strange thing happened while I was reading Francis Gilbert's book about his belief that Britain is becoming more violent and uncivilised. My husband's brother and his partner were battered by the doormen of a supposedly upmarket bar for suggesting, politely but firmly, that the sentence "Please drink up now", addressed to my sister-in-law, needn't be completed with the words "you fucking slag" in order for it to be effective. Until I saw their bruises (now fading, unlike their still vivid rage), I had been sceptical, if not about Gilbert's account of his various experiences as a victim of casual thuggery, then about his argument that it could happen to any one of us at any time.

Like Gilbert, an English teacher whose previous two books give the hell-in-a-handcart treatment to the subject of poor classroom behaviour, I live in the East End of London and use the same night bus as the one on which he was assaulted by a teenager a few years ago. Unlike him, however, I'd never even seen, never mind been a victim of, predatory gangs that call themselves names such as "Lords of Stratford Cru" and which prowl up and down the buses, beating up anyone who doesn't give them their cash and iPod. Gilbert's duffing-up on the N8 from Leytonstone seemed more like bad luck, exacerbated by a possibly drink-fuddled earlier decision to sit on the top deck with only a group of shifty boys - all black, he hastens to point out - for company.

Now I'm not so sure. Gilbert does have a point to make about the way in which Britain's public spaces often feel far less safe and inviting than they should, but he hammers it home so artlessly that you are less inclined to be swept away by his polemic than to run off in the other direction. Yob Nation, although energetic and mostly eager to examine both the root causes and effects of yobbish behaviour, is as shrill and self-righteous as only a book written by a schoolteacher could be.

Gilbert opens with a statement of his credentials - his dad was verbally assaulted and punched in 1979; he was physically assaulted in 1999: therefore Britain has become a "yob nation". He goes on to argue that the main reason many British people enjoy stoving each other in is that new Labour is a bunch of manipulative bullies. Look at that nasty Blair, says Gil-bert; he pushed to the front of the mourners' queue at the Queen Mother's funeral. (Many would think that going to war in Iraq was a nastier thing to do, but still.)

His narrative approach is to try to find a parallel in the ruling class for every example of public moral squalor among the lower orders. In Gilbert's version of Britain, such a class really does exist - in the form of army officers who think it a useful rite of passage to make their junior charges piss themselves at official dinners, City brokers who like to humiliate each other and, Gilbert's (least) favourite, anyone professionally associated with the new Labour government. This is because, to his mind, the middle classes, with a few dishonourable exceptions, are the blameless and victimised filling in a social sandwich, wedged between braying toffs and feral proles. The upper slice eggs the lower on in ever lewder, ever more violent acts of what he calls antisocial "parading".

Gilbert visits Cardiff on a Saturday night and Ayia Napa during the summer season, finding in both places a seething, spangly-dressed mass of women who, according to local barmen, "think nothing" of shagging in the street. He catches up with Scottish gangs that model their graffiti tags on Nazi symbols. He meets genuinely brave and spirited people who love the place they live in and would rather see off antisocial neighbours than give up and move away. These are the book's best chapters, allowing a wide range of people to comment on their experiences of thoughtless or nasty behaviour and giving the gentle, no doubt scandalised, reader a chance to reflect on its causes.

There are other times when Gilbert’s polemic becomes nothing more than an extended anti-Labour rant. This is where his argument goes, like a hooded teenager after your mobile phone, off the rails. Alastair Campbell seems to bear most of the blame from Gilbert, with public drunkenness, scary teenagers, women with their baps out and loud swearing all laid at his feet alone. He is painted as an even worse version of Kelvin MacKenzie and Richard Desmond, who, Gilbert writes, have used their power in the newspaper industry to show their disgust at the “liberal elite”, just as Campbell dismissed new Labour dissenters as posh softies.

Keen liberal elitists will detect an unpleasant strain of “Forsooth! The savages!”-style racism in some parts of this book. The boys who ruffle his feathers on the night bus have “cheeks sculptured out of ebony”. Quite apart from the fact that it ought to say “sculpted”, this sounds like the diary entry of a Boer war officer who fancied himself as a poet. The teenagers who sit on the wall of a middle-class north Londoner’s house, infringing his privacy and causing him grief, are deemed to lack the values of reason and decency because they are Somali, not because they are at an age where the concepts of reason and decency are about as familiar as a vacuum cleaner or the dial on a washing machine.

The sculptured/sculpted clanger is one of many in a book full of truly lazy errors. To list a few: Johan Cruyff is misspelt “Johann Cruff”, Ebbw Vale becomes “Ebw Vale” and the former Transport for London commissioner Bob Kiley is known here as “Bob Kylie” (he should be so lucky). It may be pedantic to point all this out, but it is such sloppiness that Gilbert, in his books, seems to deplore in British society as a whole. As he himself might observe, if an English teacher with a horror of poor standards in public life can make mistakes of this sort, there is no hope for the rest of us.

Lynsey Hanley’s book about council estates will be published by Granta

in January 2007