He added a postscript: 'Must find Madiba a job, because old men get up to mischief.” That, too, has proved not entirely flippant.

For the first time since he left prison nine years before, Mandela became in 1999 a private individual without any political position. By then he had been happily married for a year to his third wife, Graça, the widow of Samora Machel of Mozambique, and was enjoying his grandchildren and great-grandchildren, moving between his house in Johannesburg, his country retreat at Qunu and Graça Machel's mansion in Mozambique.

Machel is a strong character, a politician in her own right, and Mandela likes to pretend that she dominates him: 'At least she allowed me to keep my surname.”

But she has provided him with the kind of support he did not enjoy from his second wife, Winnie: 'I want him as a human being,” Machel told me. 'He is a symbol, but not a saint. Whatever happens to him, it is a mark of the liberation of the African people.”

There is a constant paradox within his character. While he claims he wants a quiet life, he is also still drawn to the public stage. While he wants to give other people the chance to take the spotlight, he remains one of the most famous men alive. He's still driven to have more experiences, to catch up on his 26 lost years in prison. He's become more, not less, impatient, an old man in a hurry.

'I have retired,” he said at 84, 'but if there's anything that would kill me it is to wake up in the morning not knowing what to do.” Machel tried to make him relax, but she soon changed her mind. 'I realised I was making a mistake,” she told me. 'He needs to be very busy. He is quite clear that if he slows down he will feel depressed. He'll feel he is not needed any more.”

In 1999 he established the Nelson Mandela Foundation, which has provided his base. His loyal Afrikaner secretary, Zelda le Grange, who comes from a very conservative nationalist family, organises his endless meetings, flights and phone calls to the world's leaders. He keeps crossing the world, particularly to Britain, the US and the Middle East, often in a private plane provided by one of his rich friends, such as Prince Bandar, the Saudi ambassador in Washington.

He has embarked on writing the second volume of his memoirs, covering his presidential years, with help from his old colleagues. He's determined to write them himself, without being ghosted, and he conducts his research with very personal methods: he rings up old friends and even former enemies, such as FW de Klerk, to ask for their recollections of crucial meetings.

But he also loves meeting showbusiness heroes, sportsmen and film stars. In his last years in prison, he enjoyed watching Hollywood films, and he's still thrilled to meet real-life stars such as Whoopi Goldberg or Whitney Houston, whom he welcomed with outrageous flattery ('I'm only here to shine her shoes”).

His more solemn colleagues complain that he's a sucker for famous faces who have no political importance but, in my view, he's merely radiating a wider love of life, beyond middle-aged men in suits. I often feel he's reliving his own youth in Johannesburg in the 1950s, when he was not only a politician, but a township hero, ladies' man, dancer and boxer.

Whenever he introduces me to others, he says: 'I first met Tony in a shebeen.” He still loves talking about the old black musicians and Drum writers and his boxing days. When I was talking to him in London two years ago, we were interrupted to be told that another visitor was waiting, the boxer Frank Bruno. Mandela wasted no time breaking off our interview.

However, he's more lonely now. As president, he was at least 30 years older than most of the politicians in South Africa and most of his contemporaries are dead.

He often looks his age. Away from the cameras, he can suddenly look exhausted and sad; with his staff, he can be irritable. He sometimes loses his place in written speeches, though he makes a joke of it: 'Unlike some politicians, I can admit to a mistake.”

But he retains a powerful will to live. In 2001 he was diagnosed with cancer of the prostate, but after intensive treatment, he soon appeared fully recovered. 'Very often the doctors are wrong,” he assured me later. 'But if cancer gets the upper hand, I will nevertheless be the winner. In heaven, I will be looking for the nearest branch of the [African National Congress].”

Mandela often reflects on his past career, sometimes with remorse: he remembers his earlier years as a struggling and quite arrogant young politician and feels guilty about neglecting friends who have helped him on his way up.

He worries that his political colleagues are being forgotten while he's so much honoured. He was shocked that university students had not heard of Oliver Tambo, his close friend and law partner, who had been the president of the ANC in exile while he was in prison, and who died in 1993.

Mandela went out of his way to praise Walter Sisulu, his first mentor, who had transformed the ANC in the Fifties, and who died in May. 'He has not occupied any great position,” Mandela said at the time of Sisulu's 90th birthday in 2002, 'but he stands head and shoulders above any of us, because he had two qualities: humility and simplicity — and steel in his soul.” When Sisulu died, Mandela acknowledged his most crucial influence. 'By ancestry, I was born to rule,” he said, but Sisulu 'helped me to understand that my real vocation was to be a servant of the people.”

Could Mandela really have been content to take a back seat in South Africa? He warned his colleagues after he retired that he would feel free to criticise the leadership 'as an ordinary member of the ANC”. But he knows he is no ordinary member. He remains the most famous South African, pursued by cameras and journalists reporting anything controversial.

He is careful not to upstage or embarrass his successor, Mbeki. He's more careful than Margaret Thatcher was with John Major, or Winston Churchill with Anthony Eden. He largely avoids commenting on domestic affairs and, when he travels abroad, he talks mainly about the need for reconciliation and peacemaking.

But during his years as president, he had strained relations with Mbeki, who was his deputy. He emphasised to me that the choice of his successor was not made by him, but by the ANC and its allies. He was worried privately that Mbeki was too suspicious of his colleagues, too dependent on a few cronies.

And, in retirement, his relations have become more tricky. At public occasions together, Mandela inevitably overshadows Mbeki and often wins more applause. In public, Mandela has begun to make remarks that appear to go against Mbeki's policies, while in private ANC meetings he can be critical.

'I don't want to be a praise singer,” he explained after one closed conference. 'I want to be objective, and I did indicate his weaknesses, which was unpalatable to many members.”

Mbeki, in turn, has become more obviously resentful of the prominence given to his predecessor, who looms above him both politically and physically. Sometimes, he omits Mandela from state occasions, sometimes he is slow to return his phone calls.

As president Mandela was very careful to be punctual with visitors, determined to contradict the reputation of black leaders for keeping 'African time”. He sometimes resents Mbeki's less scrupulous attitude to timekeeping. When Mbeki arrived very late at a Mandela family wedding party, Mandela could not resist a thinly disguised reproof.

However, it is Mbeki's handling of the South African Aids crisis that has provoked the most obvious tensions. Mbeki was taking far too long to face up to the problem and to publicise the danger. Mandela was impatient for bolder action, but he himself was not blameless on the matter.