Paul Vallely: His health has faded, but the aura remains

Since his retirement Nelson Mandela's iconic status has only grown. He has travelled the world, meeting ordinary people and national leaders, attending conferences and visiting charities and everywhere collecting awards. He has been voted the man the world would like to see as its president. Everywhere he is greeted with extraordinary combination of awe and affection.

Mandela is one of those individuals who, when he enters the room, seems to have about him a golden aura. Not the televisual halo of celebrity but something which emanates from deep inside. It seems to make those in the room feel somehow blessed by his presence.

He looks to draw the best out of everyone he meets. "Sometimes it falls upon a generation to be great," as he told the Make Poverty History movement from the platform in Trafalgar Square in 2005. "You can be that generation."

So it is entirely in keeping with the spirit with which he encounters the world that, as he arrives in Britain for the long-delayed unveiling of his statue in London, Mandela will take the opportunity to beseech Britain's black high achievers that they must beware of cutting themselves off from the less fortunate members of the community from which they sprang.

Mandela's moral authority grows from the extraordinary magnanimity he displayed to the white community on his acquisition of power in South Africa in 1994. His gentleness and wisdom were key in preventing that conflict-riven nation from descending into a post-Apartheid bloodbath of revenge and recrimination. Spending 27 years in prison had inculcated the tolerance and compassion of a secular saint. It also enabled him to shrug off power after just five years in office.

In the early years of his retirement he engaged still in politics, criticising the Mugabe government in Zimbabwe in 2000 and involving himself in peace negotiations in the Congo, Burundi and elsewhere. In 2003 he criticised the foreign policy of the Bush administration, particularly over its war in Iraq and its undermining of the United Nations.

But he threw his main energies into the fight against Aids, of which his son, Makgatho, died in 2005.

He had his own health problems. Diagnosed for prostate cancer in 2001 he underwent radiation treatment. In 2004 he announced he was retiring from public life to spend more time with his wife, Graca Machel, whom he had married on his 80th birthday in 1998. He wanted, he said, to engage in "quiet reflection".

Madiba, as he is known in his native land and well beyond, now walks slowly and deliberately with the support of an ebony-coloured cane. But he has never been able to throw off his sense of public service. On his 89th birthday last month he announced the formation of The Elders - a group of elder statesmen including Desmond Tutu, Jimmy Carter, Li Zhaoxing and Muhammad Yunus - to bring their wisdom, integrity independent leadership to bear on some of the world's most intractable problems.

"Together," he said, "we will work to support courage where there is fear, foster agreement where there is conflict, and inspire hope where there is despair." Among them there is none more revered than Nelson Mandela.

Paul Vallely was co-author of the report of the Commission for Africa