Many of us should have spotted the early-warning signals when we read Andrew Morton’s Diana: Her True Story and, having thrown up, started to gobble it all over again. By the time we were binge-reading Lady Colin Campbell’s The Real Diana, or the unforgettably nasty The Housekeeper’s Diary, almost retching as we turned the pages but unable to stop cramming in every last sordid detail, we were on a hopeless spiral. Even ready-spewed vomit such as James Hewitt’s caddish Love and War, or Paul Burrell’s The Way We Were, could still lure us. Surely, you would think, there is enough stuff out there already? Last year, Sarah Bradford provided a magisterially sensible book that seemed unimprovable.

But I am sorry to tell you that every previous Dianologist must now take a back seat. Addicts are about to be offered a feast such as they never had before, and some of it will actually stay down. Back from New York, on chariots of pure brass, comes the Queen of Gloss. Tina Brown’s The Diana Chronicles is not a book on Diana. It is the book. Not only does it put the story of Diana in its proper historical context of British politics, journalism and the changing mores of the past quarter century, but it is also a perfect example of the nosy-parker’s art. It conveys, better than anything I have ever read, the basic intelligence of its subject. Di knew she was dicing with disaster when she chose the tabloid press as the means by which she would rise beyond megastardom to sex goddess, saint and martyr. Yet the instinct was right. There’s often more truth in the lower ends of journalism than there is in its stuffier upper echelons. Again and again, this book exposes the lies told by Buckingham Palace and the collusion of public-schoolboy editors in those lies. Glossy she may be, but Brown – the former editor of The New Yorker – has all the skills and instincts of the gutter newshound.

So, what’s new in this book? Let’s start with the Blonde on the Train. In November 1980, before the ill-fated pair were married, the royal train was spotted in a siding in Wiltshire. A blonde arrived in a car and spent the night with the Prince of Wales. There were the usual palace denials. The tabloid press assumed it was Di. Woodrow Wyatt, wrong on almost everything, put about the rumour that the woman on the train, which had stopped 20 miles from Bolehyde Manor, the Parker-Bowles residence, was Camilla.

It became the orthodoxy among Dianologists that the shameless Camilla had slept with Charles just when he should have been initiating his virgin bride into the arts of love. But, says Brown, Diana was the blonde. If it had been Camilla, would not Di have used this fact against Charles in her post-Morton propaganda? Better still, Brown has the car’s registration, as given to the palace security. It was Frances Shand Kydd’s Renault, often used by her daughter Diana.

New is the detail from Mary Robertson, the American who employed Diana Spencer as her son’s nanny, that the lissom aristocrat once casually wolfed all the meat from a stew left on the stove for her boss’s dinner – an early warning perhaps of bingeing to come. New, too, is much of the detail of Diana’s phones being bugged. Brown is good on the differences between Squidgygate and Camillagate: the latter came out because of the bad luck that dogs all that Prince Charles does, but the former was deliberately leaked by the intelligence services.

The indiscretions of formerly loyal servants are glorious. Who will not cheer on reading the “off-the-record interview” with a courtier who claims to believe that Diana’s most frequently quoted words to her butler Paul Burrell – “You are my rock” – were actually “You’re wearing my frock.” And what about the Queen Mother’s reaction to Di rushing to the deathbed of her friend Adrian Ward-Jackson: “Why can’t she take on less gloomy things?”

New, too, are details of Diana’s weight loss after her first holiday as a royal bride at Balmoral: she went from 10st to 8st 12lb, provoking a row which ended when Charles flung her gold wedding ring at an aide with the barked command, “Get it made smaller.” New are the details of Charles’s tantrums, with material supplied anonymously about the Prince of Wales hurling antique clocks around and, on a visit to Althorp, breaking a window with a chair leg. And new is confirmation that Diana’s first extramarital affair was with her personal protection officer Barry Mannakee. Nine months after he left her service, he was dead in a motorcycle accident (“bumped off” in Diana’s view). New is the fact that Princess Anne nearly wrote to her brother in 1986 to tell him to “stop humiliating his wife” – the Camilla affair now being something in which all the horsey set colluded.

New, and most poignant, are the details after Diana’s death. We hear Prince Philip’s anxious voice from Balmoral – “Our worry at the moment is William. He’s run away up the hill and we can’t find him. That’s the only thing we’re concerned with at the moment.” Another touching detail is when the Queen Mother sends her page, William Tallon, to put flowers on the coffin. When he gets there, the catafalque has been lowered and he asks why. The chaplain says, “Oh, that’s for the boys. They’re waiting next door in the vestry until you’ve gone. They are going to view her then.” Tallon wept.

These details, all new, are among masses that Brown has collected from interviews with hundreds of witnesses. We hear Mary Clarke, Diana’s nanny, opine that the royal family turned “a practical, warm little girl into a basket case and then rewrote early history to justify it”. But we also see Di, on the eve of her wedding, larking about on a bike in the servants’ quarters of Clarence House singing, “I’m going to marry the Prince of Wales tomorrow!” And there are joyously irrelevant details never unearthed before, such as the Queen Mother on a naval vessel, heading for the castle of Mey where she was to give her daughter a picnic, sending a flag signal to the royal yacht Britannia – “Dearest Lilibet, Bring lemons, have run out.”

The truly impressive thing about the book, however, is its wisdom. It is full of good mots, such as “Diana’s inferiority complex became her greatest asset.” Brown sees that the great surge in the popularity of the touchy-feely princess coincided almost exactly with the Iron Lady’s attack on the weak. “In the wards of hospitals, in the run-down homeless shelters where the people left behind by Thatcher’s revolution cried out for help, Diana rediscovered her own big heart.” This may nauseate you, but it is true. The book chronicles a deeply damaged, charismatic person transforming herself from an HRH into a mega-celebrity. (I liked the detail, supplied by a “close adviser of the Princess”, that when the Duke of Edinburgh said to her, “If you don’t behave, my girl, we’ll take your title away”, Di hit back with, “My title is a lot older than yours, Philip.” Yes, there’s a strong whiff of esprit d’escalier, but still, hurrah for the toffs.)

This book is evenhanded but it gives more weaponry to the Princess’s Party than to the old fogeys who still support the funny little prince and his boot-faced wife who, as Brown rightly says, resembles his old nanny. (Brown is “virry, virry” funny at transcribing, Kingsley Amis-style, Camilla’s voice.) It leaves you in no doubt, however, that Camilla refused to leave Charles alone, and that without her the marriage could probably have been repaired. The adulterous code of the Parker-Bowles’s “set” is evoked with chilling accuracy, as is the horrible way the Old Buffer tendency in journalism tried to debunk Morton’s book. (Smug Tory bovver boys, Brown calls them.) “Charles Moore [of the Telegraph] revised the definition of journalism on Newsnight by decreeing that when writing about the royal family ‘journalists should use hypocrisy and concealment’.”

There might be a lot of brass about this book, and the author’s boasting about the grand people she has met will raise some smiles. The volume’s only picture, incidentally, is of that charismatic blonde goddess, the author. There are howlers – Private Eye isn’t a weekly, and she muddles Westminster Cathedral and Westminster Abbey. But it is a masterpiece.

Sometimes I blush for our profession – not when it is vulgar or intrusive, but when it sucks up to politicians or colludes with the Establishment. Then a book such as this appears, which will ruffle feathers everywhere. Heartless, ruthless, relentlessly inquisitive, it made me cheer to the rafters the great traditions of the gutter press.

The Diana Chronicles by Tina Brown

Century £18.99 pp481

Available at the Sunday Times Books First price of £16.99 (inc p&p) on 0870 165 8585

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