If I were to tell you that this book is a fictionalised investigation into British secondary schools, detailing breathtaking decay, corruption, State neglect, abuse, underage sex and rampant class-A drug taking, you might wonder why the author was not being interviewed on Newsnight. If I then told you she was called Jilly Cooper, you would wonder no more.

Cooper is the queen of affectionate caricature. To tell the truth, she is almost a caricature of a caricature; a genre in herself. In Cooper world, dreadful things happen but they're not real, and happiness and fun always triumph over darkness. She is the mistress of the hyperbolised modern fairy tale, the nobrainers' Angela Carter. Fortunately for Cooper, there are many grown-ups who like no-brainers, and she remains one of the most surefire of best-sellers.

Cooper - who entertained a whole lot of us at a formative age with her socalled permissive romances: Harriet, Prudence and Bella - has latterly created the mythical upper-middle-class world of Rutshire, and in it set her epics - Riders, Polo, Appassionata et al. Wicked! is set in nearby Larkshire and features some of Cooper's best loved characters, including that impossible ravisher Rupert Campell-Black, now middle-aged and even more rude, whose children attend Bagley Hall, the famous public school.

On the other side of the tracks is Larkminster comprehensive, a school servicing the local sink estate, which is raddled, bankrupt and over-run by drugtaking and violence. When Larks is taken over by the gorgeous little redhead Janna Curtis, fates decree that she will fall in love with Hengist BrettTaylor, the head of Bagley, and the two schools will be twinned in an educational union only mildly less exciting that that of their principals ("clambering over his body like a squirrel, she kissed, caressed . . ."etc etc).

There follows a plot so gloriously silly and improbable - corruption, paedophilia, orgies and betrayal (and that's just the private school children) - that long before the end of this monstrous 846-page saga the reader is begging for mercy. None is available. This is vaudeville; this is Cooper world.

When the plot burns low, or when you can feel her losing interest, she has a Dickensian tendency to throw another handful of characters on the fire in order to make it burn brighter; or at the very least to provide opportunities for unexpected sex with existing characters. (Hence unbeatable little Cooperisms like: "Life was full of surprises. Lady Belvedon gave Stancombe the best b*** j** he'd ever had.") It is little wonder the cast list runs to 11 pages, plus one page for the animals.

As ever, her names are a memorable part of the spoof. Enter the Wolf pack, the chav kids, with names like Feral, Paris, Graffi, Monster and Kylie; and up against them the Bagley Babes, rich totty called Jade, Amber, Cosmo, Xavier and Milly. And then there's her style, florid and scatter-gun. Interestingly, the acclaimed crime writer Elmore Leonard, interviewed on Front Row this week, was expounding his rules of successful writing. On his banned list were adverbs used to modify the verb "said". Cooper is queen of this device, her work shored up by people who say things bravely, nastily, incredulously, warmly; repeat indignantly, smile cruelly and suggest timidly.

Leonard's next rule was: stay away from the Mary McCarthy line in dialogue: "She asseverated". Again, Cooper is a major, if less pretentious, culprit, creating a tedious array of people who howl, squeal, pant, beam, growl, snarl, hiss and giggle their way through life.

Another of Leonard's laws is to stay away from the weather; and yet again this is Cooper's favourite structural device. Far too many chapters open with ridiculously over-written paeons to "hedgerows slate-blue with sloes" and "newly harvested fields rising in platinum-blond sweeps to woods lush and glossy from endless rain", so much so that one feels like one has strayed into some bastardised script for Planet Earth, in which David Attenborough will get propositioned by Jade Campbell-Black high on cocaine.

So we must be honest. Wicked is too long, poorly-written, indisciplined and shallow; and it fails in its attempt to tackle issues like race, poverty and abandonment. The thing is, nobody cares, least of all the shrewd, ditsy, charming, pensioner-age Bridget Jones who wrote it, nor the fans who will devour it. In terms of sheer comic silliness and exuberance, Cooper world wins once again.

Wicked! - A Tale of Two Schools, Jilly Cooper, Bantam Press, GBP17.99.