BOOK REVIEW / The pink plastic dummy award: 'Roald Dahl' - Jeremy Treglown: Faber, 17.50

'Readers may ask the question I often put to myself when I began researching the book: should I have given up and gone away?' writes Jeremy Treglown in the preface to his unauthorised biography of the most popular children's writer of all time.

Yes, is the short answer to this. Not because it would be a particularly good thing for Dahl's dauuhter Ophelia to write the official biography that Treglown reckons he was 'morally' right to pre-empt. And not because the book's sources were distinctly limited, since the second Mrs Dahl, and most of Roald's close friends and relations, refused to co-operate. No, the reason why his undertaking was ill-advised is his complete absence of affinity with his subject.

I am not asking for hagiography. I can sympathise with Boswells who gradually fall out of love with their Johnsons. But there is all the difference in the world between Treglown's perceptive and sympathetic introduction to his edition of Robert Louis Stevenson's essays, The Lantern- bearer, and this chilly post-mortem. One can only wonder at the motives of the biographer who has revealed by page seven that he is not just unenamoured of his quarry, but casually contemptuous of his highest achievement. 'Could he have been a better writer?' asks Treglown. 'Why did so ambitious, so macho a man end up devoting so much of his life to children?'

It is high time that there was some sort of pink plastic dummy award which we could stick in the mouths of biographers of children's writers who claim that their subject 'never really grew up' (Treglown, page eight, but see also Brogan's Ransome, Thwaite's Milne, Carpenter's Secret Gardens). The truth is that great children's writers are far more aware of their own rites of passage than most adult writers; the arrested developers are the Jeffrey Archers and Barbara Cartlands of this world.

Dahl's best books were the mature fruits of his parenthood; the combined perception of what his own childhood had been and how his children were experiencing theirs. Bruised and smarting from the deaths of his father (he was four) and a seven-year-old sister, he then had to undergo the rigours of English prep schools and Repton at its roughest, quite a shock for an independentminded Norwegian. The sour brilliance of his early short stories reflects the fact that he took some years to lose his grudges against the human race.

But the agonies he suffered from the death of his own first daugher at the age of seven, and the brain injury dealt to his two-year-old son in a traffic accident, concentrated his mind wonderfully on the importance of children. His own mission in life became to inspire young people everywhere. The most memorable anecdote in the book is of Dahl climbing up outside his children's bedroom window to blow the curtains, bringing to life a story he was telling them about a big friendly giant who sent children good dreams.

Treglown does not see things like this, as he picks his way fastidiously through the rumbustious, tragic, often outrageous facts of Dahl's long and lively life. He is like a missionary curate in the 18th-century stews, sniffing nosegays of gossip rather than engaging with real relish with the often infuriating but outstandingly talented Norwegian - half berserker, half bard. He does not find his jokes funny. The few genuflections he offers seem to be based on awe at the sales of the books rather than on respect for their contents.

The book is a blissfully easy read - Treglown writes well, in clear, uncluttered prose. But his aim is to portray Dahl as 'a capricious tycoon' rather than a great writer, to debunk the 'myths' that he claims Dahl put about concerning himself in Boy and Going Solo. Sure, Dahl was a fighter pilot, but Treglown emphasises that he didn't shoot down that many planes. Sure, he was irresistibly attractive to women, but he secretly hated them. Sure, he pulled his first wife Patricia Neal round from the stroke she suffered with miraculous speed - but didn't he rather enjoy bullying her? Sure, he was a philanthropist, but wasn't he just angling for a knighthood? Sure, he was a good writer, but not above plagiarism, and his best work was (an astonishing claim) largely thanks to the creative editing of Stephen Roxburgh.

Treglown may not be altogether to blame. Much of the sourness that pervades the book could be the result of the possibly ill-advised silence of Dahl's best friends and closest relations: we hear too much from ex-publishers, discarded friends, his first wife. But there are obsessively reiterated grudges. The racist aspect of the dark-skinned pygmy tribe of Oompa Loompas, now politically corrected to rosycheeked bearded little hippies, is cited no less than seven times. Charges of anti-semitism are also repeated, even in the face of Sir Isaiah Berlin's wise observation that 'Dahl's opinions were essentially fanciful . . . he could have been pro-Arab or pro-Jew. There was no consistent line.' Finally there are recurring sneers about Dahl's sexuality and odd jeers at his advancing baldness.

For the nonce, Dahl's own books will have to remain his true testimonial, but just occasionally Treglown is succinctly generous: 'Genius he revered. Next came courage, practicality, and what he called sparkiness. These were his own qualities, and those which his books encourage readers to admire.' In the last chapter, he seems genuinely moved by considering Dahl's death and the huge hole it left in the extended family of aunts, cousins, brothers and sisters in the Buckinghamshire 'Valley of the Dahls'. His closing image of Dahl is of 'his favourite vegetable, a large, handsome, tough-skinned, many-layered onion' placed on his simple hillside grave. It reads as a belated apology for his failure to get to the heart of the man.