Jack Straw is a supreme connoisseur of politics and his memoirs are for political connoisseurs: very much in character, crafted with literary elegance  erudite, forensic and fascinating. Always a consummate politician  possessed of "guile and low cunning", as his old ministerial boss Barbara Castle memorably put it  his book is a tour de force through the fluctuating fortunes of the Labour party from the mid-1960s to the 2010 election defeat.

Our two stories ran in parallel, but on quite different trajectories, from youth radicalism to cabinet office. In his early 20s, Jack was the bright president of the National Union of Students when in 1969-70 the anti-apartheid campaign I found myself leading burst on to the rugby and cricket fields of Britain with direct action against all-white South African teams. He was supportive but careful to distance himself from our controversial militancy.

His account, laced with memorable anecdotes about Labour's tortuous journey into self-destruction in the late 1970s and early 1980s, and then eventual recovery and success in the 1990s, is a sound guide to outsiders wanting some insight into this crucial period. He is rightly generous to Neil Kinnock who, he remarks persuasively, would have made an excellent prime minister. But he also rejects the conventional wisdom on Kinnock's successor, the widely admired John Smith, with whom he had a breach when he bravely argued for the abolition of the iconic Clause 4 of Labour's constitution nearly two years before Tony Blair reformed it. Straw believed Smith was not fit to be prime minister. The reason, he rather brutally gives, albeit "with some trepidation": Smith's heavy drinking. Such frankness about senior colleagues applied also to the Commons office of Mo Mowlam, "whose floor was littered with her underwear, and who might, if you were unlucky, suddenly decide, in the middle of a conversation, to change some of it".

He is also disarmingly but engagingly revealing about the pain of his father's anger toward his mother (never witnessing "any tenderness between them") and then his father's abrupt departure, leaving her alone to bring up her children. An even more startling revelation  especially to those like me who worked closely with him in government  was: "I'd always been prone to 'impostor syndrome' and felt what I had achieved was bound to be taken away from me."

He gives a real insight into being a cabinet minister  what the Private Office is like, the ministerial car drivers, the close protection officers, and the role of cabinet committees  laced with exquisite incidents that carry the reader along.

With an impressive grasp of history and a deep Labour party hinterland, he stood out among younger, more technocratic ministers. I found him commendably outspoken in cabinet, not least over the growing collapse in public trust suffered by both Tony Blair and Gordon Brown's governments. But then Jack also lost the trust of Blair because of his manoeuvring on Europe and a calculated shift of allegiance to Brown  to be arbitrarily demoted after five years as a respected foreign secretary, though his own explanation is growing differences over the Middle East.

As a formidable constant in top cabinet posts throughout Labour's 13 years in government  home secretary, foreign secretary, leader of the Commons and lord chancellor  he is well placed to give his take on the dominant issues, including Iraq, and the frustrated plots of colleagues as Gordon Brown's premiership disappeared into a quagmire. He ends with a hilariously self-deprecating description of getting lost on London's buses and learning to drive again, after 13 years of being guided and transported by protection officers.

A big hitter with acute political antennae, he nevertheless gained a reputation for delivering legislation that bit back in unexpected ways; his well-intentioned but deeply flawed 2000 act reforming party financing a good example. A senior Labour MP was recently acclaimed by colleagues when he quipped sourly: "We need a one-clause bill to repeal all Jack's acts."

As a self-confessed "anorak", Straw had a nerdish obsession for factual detail, which often got in the way of his ability to win an argument. But his photographic memory and prodigious appetite for devouring official documents left colleagues in constant awe. He was also good to work for, delegating well, listening and encouraging a team spirit.

Some memoirs by former Labour politicians generated headlines and big serialisation fees  promptly to disappear, quickly remaindered. This book will stand the test of time. Straw's account of Labour's journeys in and out of power over nearly five decades is a must for serious students of government and politics.

Peter Hain's own memoirs Outside In (Biteback) are just out in paperback

When Barbara Castle appointed the young Jack Straw as her special adviser at the social services department in 1974, she said she wanted him for his "guile and low cunning". She was not, presumably, disappointed. Straw went on to be a Labour frontbencher  in either the cabinet or shadow cabinet  for 23 consecutive years. In all that time, he resisted categorisation into any of the party's many strands of opinion and faction. After becoming an MP in 1979, he joined the leftwing Tribune Group and voted for Michael Foot as party leader. He also voted for Tony Benn as deputy leader against Denis Healey, a decision which, in this book, he rather ungallantly attributes to Castle's flawed advice. Thirteen years later, he managed Tony Blair's leadership campaign. Thirteen years after that, he managed Gordon Brown's.

He was privy to most of the serious plotting against Brown and even emerged as the favourite not only to succeed the failing leader but to deliver the bad news to him. But a visit to Downing Street with the deputy leader, Harriet Harman, amusingly recounted in this book, ended with Straw merely telling Brown to "widen the political circle involved in election planning". Bennite, Kinnockite, Cookite, Blairite, Brownite: Straw somehow avoided all the labels, even though, by publishing an anti-clause IV pamphlet in 1993, he was in some respects an early outrider for Blair.

To dismiss Straw as an unprincipled and narrowly ambitious politician is to miss the point. Straw is tribal Labour; his maternal grandfather was a Transport and General Workers' Union shop steward, his mother a Labour councillor. At 13, he decided, while delivering leaflets in pouring rain during the 1959 election campaign, that he'd like to be an MP. The abiding principle of Straw's life is that Labour should be in power. What it should use power for is something he hardly seems to think about. He has never claimed to be a conviction politician. Rather, he is a managerial one, as was evident even when he was National Union of Students president, elected on a "radical" ticket but never seen without a tie. As a student politician, he worked with the Communist party, because he admired its organisation and discipline.

He records, with some pride, his skill at avoiding direct questions and showcases Castle's "guile and low cunning" comment below a chapter heading. He admits (five times, as meticulously recorded in the index) to "anorak" tendencies: his strongest passions are mostly to do with constitutional, administrative and electoral arrangements. He supported abolition of clause IV not because of strong views about the merits of private against public ownership, but because he thought it would help Labour get elected. As shadow home secretary, and then as home secretary, he proposed illiberal policies, such as increasing police powers and restricting jury trials, mainly because he didn't want Labour to be thought "soft on crime". By reputation a long-standing Eurosceptic, he unhesitatingly assured Blair that, if there were a referendum on the euro, he would support the government line. He dismisses an "ethical foreign policy" as an "unhelpful" label. Referring to Blair, he observes acerbically that "a 'world view' is a dangerous and misguided notion."

The big philosophical issues of politics  the role of the state, the limits of markets, the merits of egalitarianism  are scarcely on Straw's radar. Big pictures and big ideas are not for him. His habit is to amble along in roughly the same direction as everyone else. Still an MP, Straw voted for David Miliband as Labour leader, as most Labour MPs did, but now, like most Labour MPs, thinks Ed has "shown himself to be decisive and  made some difficult moves well".

These memoirs are better written than most. There is ample gossip and genuinely funny stories, of which the best concern a chief whip who made his point by squeezing Straw's testicles, and health and safety officials who stopped the union flag flying on Portcullis House. As well as waspish observations about personalities  Charles Clarke is "a quixotic contrarian"  there are revealing anecdotes. For example, when the Labour government won a Commons division on top-up university fees by just five votes, Straw warned Blair not to push his luck too far. "'Jack,' he replied, with blue eyes blazing, 'I'm always lucky.'"

The most absorbing part of the book concerns his traumatic childhood and early adulthood. He recalls, without self-pity, how his parents quarrelled bitterly and eventually parted; how, aged nine, he saw a maternal uncle beat up his father and, next day, found his father attempting suicide; how he was initially so unhappy at boarding school (to which he won a free scholarship) that he ran away three times in one week. Later, Straw's first wife developed anorexia and their child died at six days old. Straw himself suffered chronic tinnitus after an ear infection. Depression led him to consult a psychoanalyst whom he still sees occasionally.

But the section that will attract greatest interest is disappointing. He describes his decision, as foreign secretary, to support an invasion of Iraq as "the most difficult and momentous  I've ever made". He could, as he says, have stopped UK involvement. His explanation of how he reached his decision, however, is unconvincing. We learn almost nothing about the thought processes that led a former Aldermaston marcher  whose father was a conscientious objector in the second world war, whose mother joined the Peace Pledge Union in the 30s, whose second wife and children opposed the Iraq invasion  to support the most controversial deployment of British military force in nearly 50 years. Straw has nothing to say about American use of (and possible British complicity in) extraordinary rendition. Nor does he comment on allegations that US neoconservatives wanted him out of the Foreign Office; he attributes his bitterly resented demotion in 2005 to Blair's jealousy of his close relationship with Condoleezza Rice, the US secretary of state.

Perhaps there were no thought processes. Straw is a reactive politician, not a reflective one. There has always been a curious lack of passion to his politics and, on his own admission, he tends, because of his childhood, to bury his feelings. He says in a footnote that he was confirmed in the Church of England in his 40s, but gives no clue as to how deep his religious beliefs go.

The secret of what makes Straw tick may lie in his school holidays, when he worked for his uncle as a plumber's mate. He learned "to cut, bend and solder pipes, and much else". That was how he approached government and policy-making: he aimed to keep the water flowing and the boiler flues clear. He was New Labour's safe pair of hands, its trusty plumber, a much more competent than average minister. The conception of the project may have been flawed, fatally so in the case of the Iraq war. But it isn't a plumber's job to worry about the architecture.