Diarists, of course, come in all shapes and forms and from all walks of life. Similarly, the reasons why people keep diaries vary enormously. Some use their diary as an aide-memoire, others in lieu of the confessional, still others - in this financially volatile age - to give their pension a boost. ThoughtheauthorRobertHarrisonce quoted to him Mae West's famous dictum - "I always say, keep a diary and someday it'll keepyou"-Campbellhasdeniedthat money was his motivation. Which, because hehasreputedlyreceivedmorethan £1 million for his diary, may be treated with appropriate scepticism. However, Campbellinsistshehaslongbeenadiarist, starting when he was a child growing up in Yorkshire where his father was a vet. But when he began to work for Blair, he says, whathadbeenanoccasionalhabit "became a conscious decision to record events as closely as I could. I kept a diary every day I was there, usually, though not always, recorded on the same day, never more than a day or two behind."

Not that there is anything particularly unusual about that. If, as is often claimed, we are never more than a few feet away from a rat, we are also rarely out of the company of a diarist. Politicians in particular havealwaysbeengreatdiarykeepers. Pepys, who single-handedly invented the form, was a politician, rising to high office in the Admiralty. In the 20th century many of the best diarists, such as Chips Channon, HaroldNicolsonandAlanClark-an unlikely chum of Campbell - moved and shook amongst the great and the good. Even more recently Edwina Currie revealed how she and John Major saved water by sharing a bath ("one of those cor, f*** me' jaw-dropping moments", as Campbell so eloquentlyrecords)whileinhisdiary Robin Cook chose to ignore his marriage-busting affair with his secretary, giving instead an account of how he came to resign over the Iraq war.

None of the above, however, had quite the access to power enjoyed by Alastair Campbell. That is one reason why his diaries make such compelling and incendiary reading. Another, of course, is the character of the diarist himself. In many respects, Campbell is the ideal diarist. Though he has edited his diaries down from two-and-a-half million words to 350,000 and, on the insistence of Blair, excised muchofthefeudingbetweenhimself and Gordon Brown, he is a model of indiscretion, a quality common to the first rank of diarists.

Moreover, his personal flaws are never very deeply submerged. On the contrary, he seems happy - as perhaps only someone who has had a major mental breakdown can be - to confess all. When I interviewed him in April 2004, not long after he'd left Downing Street, he talked manically and rather madly. His mantra - "pain has no memory" - was more New Age than New Labour. When I suggested he was talking nonsenseheaskedmeto"define" toothache. When I said he might become a male rival to Carole Caplin, the erstwhile topless model turned shopping guru and Cherie Blair's confidante, he snorted. As the diaries show, he was suspicious of Caplin from the outset. "My way is my way," he chanted, like a Zen Sinatra. "Your way is your way and it's unique to you." At that I half expected men in white coats to rush in and bundle him into a straitjacket.

Time and again throughout the diaries, Campbell seems to be on the brink of a relapse. He is a man on the edge, blowing his top, cursing like a dementedfanontheterracing,railing against the media, threatening to resign, fretting over his partner, Fiona Millar, who never wanted him to take the job in the first place. His diary was theonefriendtowhomhecouldtalk honestly and whose loyalty was never in question. The diary was his soulmate. Writing it, he says, was therapeutic and a way of venting frustration and anger. It was also, he adds, "a way of keeping on top of things, and giving some kind of order to often chaotic and confusing events around me".

Campbell's diary begins in July 1994, when Blair calls and asks him to become his press secretary. At the time Campbell was political editor of the Daily Mirror, a Labour fanzine. A few days earlier, following the death of John Smith and the outmanoeuvringofGordonBrown,Blairhad become leader of the Labour Party. Initially Campbell was reluctant to accept but a month later, having been subjected to one of Blair's irresistible charm offensives, he accepted.Standingontheplatformat Marseilles station, Blair, looking "very odd in a pair of holiday shorts and what looked likeasuitjacket",toldCampbellthat together they could "change the face of British politics for a generation, and change the world while we're at it".

THUS began one of the most intriguing relationships in modern British history. But to Blair and Campbell, must be added two significant others, Gordon Brown and PeterMandelson.ThisquartetwastheNew Labour equivalent of the Rat Pack, each easily caricatured, each fundamental to the redrawing of the UK's political map. "Even their eating styles weresodifferent,"relatesCampbellofBrownandMandelson."Gordona chomper with his jaws pounding backandforth,Peterlookingwithrealdisdainat the sandwich and then tearing off little pieces and popping them in his mouth as if they were aspirins."

Throughout the diaries, however, it is not thebroodingBrownorthepetulant Mandelson or even the volcanic Campbell who commands the reader's rapt attention. ItisTonyBlair.Oftenwrittenoffas Campbell's poodle, the Blair depicted in the diaries is a much more complex and potent and driven man, unknowable to almost everyone except his wife, Cherie. Early on, in February 1995, Campbell records Blair's assessment of his disciples.

"TB said he reckoned that in our own very different ways, GB, Peter M and I were geniuses, the best in our field at what we did,andthekeytohisstrategy.Butit drove him mad that we couldn't get on. I said I can get on with anyone but it has to be based on an understanding of what we're all doing. He accepted of the three of us, I was trying the hardest to make it work. But he said when GB was motivated, he had a superb strategic mind and he would be brilliantcometheelection.Peterwas brilliant at developing medium-term media strategy, and spotting trends and analysing how to react, and you are second to none at shaping message and driving it through the media. Fine, I said, but we are all flawed in our way."

Campbell's insistence on acknowledgingflawsis indicativeofhismelancholy character, which he tracestohisPresbyterian roots.Itisamazinghow Scottish he felt, he tells Jack McConnell in 1996, before coming to Scotland and being confronted by the Scottish media. The diaries contain few mentions of the land of his forebears and none is complimentary. Scottish politics, we learn, is a nightmare. The man from the Scottish Sun is "a total wanker". "Scotland, as ever, was a disaster waiting to happen."

The last remark was made on the eve of the1997generalelection.IwasatThe Scotsman at the time and Blair had given it aninterviewinthecourseofwhichhe compared the Scottish parliament to an English parishcouncil.Notsurprisingly,TheScotsmanthoughttheanalogysignificant and insulting, and said so. "It was totally dishonest," rails Campbell. "He had been making a pro-parliament point, saying that if a parish council could levy taxes, why was it such a big deal if the Scottish parliamentcould?Buttheytwistedit against us, because they were determinedtoportrayhimasanti-devolution, and it was an immediate f***ing nightmare."

Memory is notoriously fickle, but Campbell's typically hyperbolic interpretation does not accord with mine. What he seems to have forgotten is how, a year earlier, Blair "suddenlypipedup"thathewantedto make significant changes to Labour's policy on devolution, which many thought was set in stone.

Now he wanted to limit the parliament'stax-raisingpowersandinsistedona referendumbeforedevolutioncouldgo ahead.And,heexplicitlyunderlined, power devolved was power retained at Westminster. "That, he said, is the answer to the WestLothianquestion."Inlightofthe above, is it any wonder The Scotsman questioned Blair's commitment to devolution?

Campbell's responseto The Scotsman is indicative of the way he operated, which was like a child who throws its toys out of the pram without thinking about how it is going to get them back. Like his friend, ManchesterUnitedmanagerSirAlex Ferguson,hewouldneverpublicly denouncecolleagues,preferringtobollockthem behind closed doors or in his diary. One can only imagine what he was like in full flow. At Cambridge University, he concedes, he was such a complete headcase he used to headbutt the cigarette machines until they broke. Which makes the inhalation or not of illegal substances seem pallid in comparison. But it is to Campbell's credit, and to the benefit of his diary, that he is prepared to allow such things to be printed. Like Pepys confessing to pinching a girl's bum in church, it makes him more human.

It is telling, for instance, how needful Campbell is of praise. Time after time, he records when someone says something niceabouthim.Blair,whoisoften upbraided for not thanking his staff enough for their efforts, spends infinite hours geeing and cheering Campbell up, constantly telling him how much he needs him, how he can't imagine how he could cope without him. "Do you ever think you would be a better leader than me?" Blair once asked. "No," replied Campbell, "because for a start I lacked his patience." It is not a converstion one can imagine, say, Margaret Thatcher having with Bernard Ingham. Blair, though, one feels, has the measure of Campbell, knowing just when to massage his ego and when to tweak his tail.

FOR his part, Campbell cannot disguisehiscompetitiveness. "We had a football match, my team against TB's, and we lost 3-2. TB missed an open goal though."WhenBlairplays keepie-uppiewithKevin Keegan, Campbell notes that they kept it goingfor28consecutiveheaders,adding: "Though of course a professional like Keegan can head the ball towards a target in the same way most of us can throw it, so it wasn't that difficult." The rivalry reaches its apotheosis with Princess Diana who, if one is to believe Campbell, asked Blair: "What's Alastair Campbell really like?" Soon she had a chance to find out, when Blair and Campbell and she were invited to dinner at the house of mutual (and relatively humble) friends. "The atmosphere was a little bit forced at first," writes Campbell, "and I think we were all struck by what an abnormal meeting it was, and I resorted to humour early on, telling her about TB's paranoia about the neighbours spotting anyone, and saying I had tried to assure him we were in the hands of the best media operator in the world, that our operation was hopeless compared with hers, and if she wanted it quiet, it was quiet, so he had no need to worry. TB couldn't work out whether to flirt with her, or treat her like he would a visiting dignitary. He ended up doing a bit of both, but was not comfortable."Campbellwouldhaveus believe that he bested his boss, with the princess making him a cup of tea. "When she left, Cherie kissed her on both cheeks and then Diana looked at me and said, God knows what this man will do'. I shook her by the hand, and she giggled."

Seven months later, Blair was prime minister and Diana was dead. "We agreed that it was fine to be emotional, and to call her the People's Princess." This speaks libraries for the manner Campbell and his master operated: the ersazt spontaneousness, the imperative of a soundbite, the shameless desire to make Blair hero of the hour. Judging by the scale of the mourning, it worked.

WISELY,callsfora halt to campaigning on devolution were rejectedbythen Scottishsecretary,DonaldDewar."TheScots," records Campbell, "were not so wound up by it all." He, meanwhile, was tearful and emotional. Nevertheless Diana's death was an opportunity for Blair and Campbell to define the direction of New Labour and to set out their stall. For Campbell, helping the royals out of a hole of their own digging was an odd position in which to find himself. "On the other hand, it was bound to be afascinatingperiod,andagenuinely interesting professional challenge."

Reliving those heady, incredible, crazy days through the eyes of Campbell is like being in the dock for a crime you know you committed but insist you didn't. Perhaps it is just Campbell's warped perspective, but the sense and the scale of barely-managed chaosisscary.BeforeBlairiselected Campbell reflects on how it is amazing "the way the press thought we ran this well-oiled machine, but inside the machine ... it felt very rickety". Once in government, things did not get any calmer. On the contrary, the pace quickened, the demands grew and the need to corral the feral beasts in the media looked ever more impossible. Campbell's ire towards the media is incandescent. Variously, we are wankers, c***s, bastards, beneath contempt. When Dewar dies in October 2000 the Daily Record asks if Blair will write a piece. He agrees but says it will be offered to everyone. "Fine," replies the Record, "but it would be nice to get a couple of gimmicks just for us." Campbell snorts: "And they wonder why I loathe them."

But it would be wrong to assume that his hatredwasconfinedtothepress.Roy Hattersley, a former deputy leader of the Labour Party, is "a fat pompous bastard", while he despises Clare Short with a venom and finds George Galloway "repulsive". All of them, one expects, will be happy to accept the compliment. None is one of what Blair calls "serious people", ie these who accept Cabinet responsibility and toe the line. One of the few people to escape censure is Des O'Connor - "He was much more charismatic than I imagined, had real presence" - whose part in the Blair era history may find it difficult to footnote.

The longer Blair remains in power the less one feels he is in control of events. In his first term, the honeymoon was prolonged and hiccups, such as the Robin Cook scandal and Welsh secretary Ron Davies'smisadventureonClapham Common with rent boys, had little impact on the government's popularity. Campbell, it seems, was coping, just. Towards the end of that term he began to talk about quitting. But he endured and was still there in 2003 when Blair threw his lot in with George Bush and decided to invade Iraq on the pretext that Saddam Hussein had weapons of mass destruction and was preparing to use them. By day Campbell was putting out forest fires, by night, rowing with his partner, the shrewishly portrayed Fiona Millar, who was employed to ensure Cherie Blair's relationship with Carole Caplin did not generate embarrassing headlines.

THENcametheAndrew Gilligandebacleandhis allegation on the BBC that in a dossier published in September 2002, the government - and Campbell in particular - had deliberately exaggerated the threat of Saddam Hussein: the consequences of which we now live with.

"The main news overnight was lots of looting going on Iraq, the BBC hyping it for all it was worth," writes Campbell on April, 11, 2003. "Gilligan was saying there was more fear there now than there had been before. Geoff Hoon called re Terry Lloyd TV reporter. It was pretty clear US forces had killed him ... Amid all this, we had the people from The Simpsons in to record TB. The writer was a really serious type who clearly worried himself a lot about his work. He and I had been batting scripts back and forth and it was fine really, though as TB said,therewouldbeplentyofpeople willing to slag him off for doing it. But hell, he said, there aren't many perks to the job worth having, so how can you say no to a bit part on The Simpsons?"

Thanks in no small part to his diaries, which Lord Hutton insisted on reading as part of his inquiry into Gilligan's accusation over the so-called sexing up of the September dossier and the subsequent suicide of his source, Dr David Kelly, Campbell and the government were exonerated. So Mae West was right: keep a diary and some day it'll keep you. It also makes other people jumpy. When Tony Blair heard that Lord Hutton had requested to see Campbell's diaries he was at first dismissive ("a fuss about nothing") then agitated and angry. "What's in these things?" he finally asked. A fair bit of bad language, said Campbell. "How much?" A fair bit. "F***?" Yes. "C***?" Probably. "Bloody hell, Alastair." Bloody hell indeed. Where, one might well ask, is the next landmine likely to go off?