It is, said Tony Blair after reading Alastair Campbell’s diaries, The Blair Years, a book about that great historical figure Alastair Campbell, with a walk-on part by some bloke called Blair.

The story might, like so much about Mr Campbell, be apocryphal. But it is credible. There is some element of almost everything that Mr Campbell does that is, in the end, about Mr Campbell.

So why is one of the world’s most famous and most aggressive spin-doctors to launch his much-awaited book this weekend to a strange silence? No serialisation deal, no launch party – “I don’t really like parties” – and just the one television series?

For a man who made a living out of attempts to dominate the media it seems odd. But talking to those who know him best, and reading Mr Campbell’s new online blog, it is clear that something spectacular, disturbing and possibly career-damaging has happened: Mr Campbell has turned nice.

Friends told us that Mr Campbell, who had previously suffered from severe depression, had a mild bout of it for a while after leaving No 10. In that overheated summer of 2003, he was at the centre of the blaze of fury and confusion over Iraq dossiers, the BBC and the untimely death of David Kelly.

He had for a significant number of people, Labour MPs among them, come to symbolise all that was wrong with the spin or, to them, lies of the new Labour project. As Matthew Parris said: “The Project Inc has out-sourced evil, making one unfortunate man the repository of its poisons, and soon that man must slink away into the wilderness, carrying away with him sins which were never committed for his own advantage.”

After resigning, he spent long days barely bothering to get out of bed. But from this period the new Mr Campbell emerged, one for whom the personality as well as the events of the Blair years seem a matter of distant historical record.

The man who attacked, in the strongest possible terms, the New Age guru Carole Caplin, has himself undergone a “substantial process of self-awareness”, according to friends. The latest on-screen incarnation of Mr Campbell, as the almost psychotically driven, foul-mouthed bully Malcolm Tucker in the BBC political satire, The Thick of It, shown this week, was described as “a bit of an exaggeration” by his wife, Fiona Millar.

Only “a bit”? Yet now, Mr Campbell is milder, calmer, “much happier than he’s ever been before”, according to one friend.

Take, for instance, his blog entry on Thursday, in which this week he shared an encounter with his old enemy Caplin. He suddenly comes to this revelation: “I found myself realising that as time passes, you can have a different perspective on events and people.”

And what’s this, from the man who famously told Blair “we don’t do God”?

“I did feel there must have been some force of fate at work that pushed us into the same place at the same time for what, days before the book, felt like a kind of reconciliation.”

So the book has had a therapeutic role, not least because it has given him a safe outlet for his obsessional tendencies. His new blog is an obsessive “diary of a diary” about the writing and releasing of what he admits is an obsessive’s diary.

“I have to own up to being something of an obsessive and keeping my diary is just one expression of that.”

When the book is published on Monday, it will place Mr Campbell at a crossroads, in terms of his career, and possibly his psyche too. You might summarise this as a choice between politics – and the stress it places on him – and happiness. Put another way: can Mr Campbell afford to stay nice?

In the postBlair years he has made varied attempts to fill his diary. His most satisfying work has been in fundraising, capitalising on his clout and contacts from his time at Mr Blair’s side. At a dinner this week he persuaded Mick Hucknall (Mr Campbell is also a great name-dropper) to sing at a Tory businessman’s table for a £5,000 donation to his cause, Leukaemia Research. His best friend, John Merritt, died of the cancer in 1994, followed six years later by Merritt’s nine-year-old daughter, Ellie, and he has personally raised more than £1 million for the charity and facilitated millions more.

In typically determined fashion, Mr Campbell did not just stick his name on the letterhead, he captained a triathlon team at the age of 47, and recruited 3,000 other people to the Leukaemia Research triathlon: in 2003 it raised £20,000; now it raises £500,000 a year.

“If we have a problem, he has a solution,” said Cathy Gilman, the charity’s chief executive. It is a theme that crops up frequently among Mr Campbell’s friends.

“If you’re in trouble, he’s the best person in the world to have on your side,” said Lord Gould of Brookwood, who, as Labour’s pollster-in-chief, has worked closely with Mr Campbell for years and shares family holidays. “You can virtually feel him stitching up his Superman outfit, ready to help. He loves to help people out of problems.”

This is also what is calling him back to politics. Although furiously loyal to Mr Blair as Labour leader, he was not, said colleagues, similarly devoted to his policies. It was Mr Campbell who went to Scotland in the Easter before the 2005 election to mend fences with Gordon Brown and persuade him to work with Mr Blair, when the two were barely on speaking terms.

A year later he took part in a series of meetings with Mr Brown and Mr Blair to try to organise a smooth transition of power; the summits floundered after a few months. It is little known that he has quietly advised Mr Brown on an ad hoc basis ever since. The new Prime Minister calls him for advice.

For, far more than Tony Blair ever was, he is a Labourite, tribal, obsessed, steeped in Labour politics since the days of Neil Kinnock, his political hero. When he left Downing Street he decided that he would not publish until Labour was out of office to prevent embarrassment. Now he has struck a compromise deal with his conscience and gone ahead with a sanitised version. Discomfort over his change of heart may also account for the book’s muted launch.

So his diaries have been purged of what many consider the angry heart of the Blair years: the furious rows between the then Chancellor and Prime Minister. Despite his attacks on biased reporting in the press, there will be no criticism of Mr Brown within these 700 pages.

What remains, according to one who has read it, is still a detailed account of what it was like to be at the very heart of these events. “What will strike you is not how much has been taken out, but what stayed in.”

Mr Campbell is prepared for a certain amount of derision, not least from his old enemies in the media, many of whom have never quite got over him. Friends encouraged him to tone down what amounted to a boast in the book that Diana, the Princess of Wales, had a crush on him. He said he would leave it in, because you had to be ready to be laughed at a bit.

But those who care about him are nervous about his temptation to return to politics, because it also risks a return to the Mr Campbell character of the Blair era.

Yes, other ventures have not been unqualified successes: when he decided to tour regional theatres with the Alastair Campbell show, a question-and-answer session about his political life, friends were divided as to whether it was a vague success or a huge embarrassment. Many thought he was demeaning himself. He now makes money on the private speaking circuit.

Yet a more formal role in politics has its dangers. A common thread running through conversations with those who know him is that they are all slightly unnerved by him. His determination can be destructive to himself and others, as those in the media who still bear the scars of his monsterings would attest.

On a more serious level, there are critics who believe that questions remain about Mr Campbell’s role in the dossiers prepared before the Iraq war. “He is brilliant, but highly strung,” said one friend. “You wonder what his next obsession will be. He’s the kind of guy who everyone who knows him well worries about. Fiona is a saint.”

“You do have to look after him,” said another. “He is a completely extraordinary person, so driven. But you’ve got to take care of him – like many of those really brilliant people who are much better at advising others than themselves.”

In May Mr Campbell turned 50. The man who doesn’t like parties celebrated at a house in Scotland with his family and a handful of close friends. At Fiona’s request they all made brief speeches about him. Lord Gould said he possessed the qualities he admired most in people – courage, loyalty and humour. But many will have wondered what he will do next: some friends want him to turn his talents to international problems, while he himself has mentioned mentoring troubled youngsters.

As Mr Blair jets off to solve the crisis in the Middle East, Mr Campbell is without a new purpose. And there is always Labour calling him back.

“He is torn between wanting to be at the heart of things and the fact that politics is a huge strain for him,” a friend said. “But he has a blind spot here because he is so strongly Labour.”

Does he choose to give his life to Labour, or does he choose life? It is a question that even the master spin-doctor cannot, at this point, answer.

From the Campbell blog

“Question: what do Alex Ferguson, Mick Hucknall, Billie Holliday, Bill Kenwright, Carole Caplin and the artist Harold Riley have in common? Answer: they are all in today’s blog following a rare night out in Mayfair last night”

“No serialisation, no launch party . . . maybe just a reflection of the fact that apart from the Labour Party, I don’t really like parties”

On meeting Carole Caplin: “The great irony that I, who had always been worried she would do a warts-and-all insider’s account of life with the Blairs, was on the verge of doing a warts-and-all insider’s account of life with the Blairs”

On his rivalry with Piers Morgan: “I have been confused with a few people in my time and have had several people, Piers included, tell me they have been mistaken for me. But me being mistaken for Piers bloody Morgan! This surely was a low point. The fact that he is in my book a tiny fraction of the number of times I was in his is of little consolation”

On the charms of a French journalist, Christine Buhagiar: “She was on most days a rare island of beauty and elegance amid a sea of middle-aged men. Whenever I was in a situation likely to lead to me losing it with them, my friend and colleague Hilary Coffman used to suggest I direct all my answers at Christine. It is amazing how a woman’s eyes can calm a rising temper”

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