Those in high office usually retire from their punishing schedules and the lime-light before publishing their memoirs. That option was unlikely to be open to Nelson Mandela, who at the age of 75 became President of South Africa’s first democratically elected government. As the final words of this autobiography indicate, his “long walk is not yet ended”. He has committed himself to continuing his public service and most South Africans,conscious of his pivotal role in the peace process, wish him health and longevity.

This autobiography was begun, however, during a period of enforced retirement from public life on Robben Island, while serving a life imprisonment sentence for attempting to topple the apartheid state. But for political prisoners there was no retirement from politics. Mandela was encouraged to write his memoirs so they could be smuggled out and published for his 60th birthday as a contribution to the struggle. He threw himself into the task, writing secretly at night and sleeping in the day after work at the lime quarry. The manuscript was then processed on an “assembly line” with comrades commenting on each day’s material, someone transferring it to microscopic shorthand and another comrade designated to smuggle it to the outside world.

How the original manuscript was discovered is just one small story in a rich description of life on the notorious Island - known as “the University” by inmates determined to use their years there productively. Mandela’s story begins with his country childhood in the Transkei. He vividly recollects his transition from rural, tribal roots to rebellion as a young man intent on escape to city life, to gradual but inevitable politicisation. The warnings of a white liberal employer about the dangers of being influenced by the ideas of Walter Sisulu and the African National Congress were in vain.

Mandela is open about his early Africanist leanings. Despite forming what were to be life-long friendships with white and Indian intellectuals when he began to attend law lectures at the University of the Witwatersrand, he was suspicious of what he saw as a white-controlled communist agenda. In time he was to adopt a less polarised view which combined a firm commitment to non-racialism and an African National Congress which embraced people of diverse political persuasions.

Writing in prison provided much time for self-reflection. For instance, he reveals his own psychological conditioning and initial panic on finding himself in the hands of a black pilot during his first trip out of South Africa, to raise funds for armed struggle in 1962. He too had fallen into the “apartheid mind-set” and had to chide himself for inference of black inferiority.

Frequently evident is his sense of humour and irony. He comments wryly on the bizarre iron grilles that the authorities attempted to erect in court during the Treason Trial to separate men from women and whites from blacks: “Even a master architect would have had trouble designing such a structure”. There is constant evidence of Mandela’s strongly philosophical nature, often summed up in simple statements. “We fought injustice to preserve our own humanity” and “Like the gardener, a leader must take responsibility for what he (sic) cultivates”. While his language reveals a deeply embedded patriarchal outlook, he is also extremely generous spirited. He is at pains not to prejudge his warders and indeed created significant bonds with some of them. He even detects a “core of decency” in the most brutal Commanding Officer of Robben Island, Colonel Piet Badenhorst.

Probably the clearest example of this generosity of spirit is his brief account of the breakdown of his marriage to Winnie, following his release from prison. Mandela fundamentally takes the blame on himself, leaving her free from criticism. She married a man who “became a myth; and then that myth returned home and proved to be just a man after all”.

It is, however, in this latter part of the book that the inquisitive reader may feel less satisfied. Partly this is a matter of the book’s production. Mandela acknowledges the collaboration of Richard Stengel in helping edit the first part (derived from his own writing while on the Island) and in the writing of the latter section (derived from interviews).There is a shift to more formal statement and less of the intimate tone of personal commentary as he describes the extraordinary process of negotiations between oppressor and oppressed, begun while still in his prison cell.

There is, however, a deeper issue. President Mandela’s prime loyalty is undoubtedly to his political vision. While distant events may be allowed to emerge more fully, the presentation of relatively recent ones is much more politically sensitive and constrained. Other silences in the book are probably matters of oversight. There is no reference, for instance, to the International Defence and Aid Fund which provided so much support for South African political prisoners.

In all, these 617 pages make absorbing reading. They include some memorable images, like that of Mandela and his comrades after a day’s work on the Island looking “like pale ghosts except where rivulets of sweat had washed away the lime”.

It is the work of a great politician who still retains the ability to reflect on himself as a mere mortal: “The truth is that we are not yet free; we have merely achieved the freedom to be free”.

Beverley Naidoo’s latest novel for young people on South Africa, No Turning Back, will be published by Viking in the summer.