A few years ago, I was being driven with charity workers through the grimy streets of Addis Ababa. Every time we stopped at a traffic light, children's faces would appear at the open windows, begging for food and money. My colleague, new to Africa, instinctively reached into his bag and handed out his week's supply of mints and fruit pastels. “Please don't do that,” snapped one of the white expat charity workers, “we don't wish to encourage dependency.” And our enormous four-wheel-drive vehicle headed on to the Sheraton Hotel, where we parked alongside all the other Jeeps and Land Rovers serving the “donor community”.

I think of those pleading children, and the prim European latter-day colonist, every time the matter of the true efficacy of international aid is debated. Several provocative books along these lines have been published recently, notably Dambisa Moyo's Dead Aid, a polemic about how international aid is actually damaging Africa. According to these revisionist views of Africa, if there is something worse than stealing candy from a child, it might well be giving candy to a child.

Michela Wrong's reflections in It's Our Turn to Eat about Africa's inability to govern itself are certainly gloomy. But the story she tells is more interesting because she humanises the problem by exploring it through the experiences of a friend, John Githongo, an intelligent and well-educated Kenyan who convinced himself that his government genuinely wanted to eradicate corruption.

Githongo was appointed to be a sort of anti-sleaze tsar by the government formed in 2002 by President Mwai Kibaki, who was initially regarded as one of Africa's promising reformers capable of repairing the depredations of the long regime of Daniel arap Moi.

A trenchant newspaper columnist who had taken a degree at the University of Wales, Githongo was a colourful character around Nairobi with many friends within expatriate journalistic and diplomatic circles. But soon after his appointment as the scourge of corruption, it became clear that Githongo was in fact an unwitting stooge employed only for presentational purposes. There was no appetite to reform government structures, and Githongo was quickly thwarted and then traduced by those who were determined to continue lining their own pockets.

The gregarious 39-year-old bachelor became the subject of a vicious campaign in Nairobi's lurid press, where he was branded a homosexual and a founding member of the exotically named, and nonexistent, Royal Gay Society. Fearing for his life, he eventually fled, and turned up on the doorstep of Wrong's flat in Camden Town. Sportingly, Wrong, a veteran Africa hand who now seems to despair of the continent she knows so well, offered him her spare bedroom and found herself drawn into a clandestine operation to protect him in London against Kenyan agents who might seek to do him harm.

The experience took a terrible toll on Githongo, who becomes a pitiful figure in exile after an academic billet was found for him at Oxford. Despite the hours of tapes he has made detailing who was stealing what, his evidence is not used by the British government to clean up its aid operations in Kenya or elsewhere. Zimbabwe is a licensed kleptocracy and its captive population is experiencing the inevitable consequences. Corruption has taken deep root in South Africa, where the Scorpions anti-corruption unit has been disbanded by the ANC, after getting too close to men in power.

Wrong is scathing about how counterproductive the international aid effort has proved to be. New Labour has eased diplomatic pressure on African despots, while striving to achieve bizarre self-imposed targets in giving away ever larger amounts of taxpayers' money. The British high commissioner or ambassador in an African capital is a diminished figure these days. Staff of the Department for International Development have bigger budgets and better equipment.

The British government doesn't really care about corruption in far-off countries. Politicians prefer to be photographed with Bob Geldof and Bono rather than tell the African elites to take their fingers out of the till. Githongo, meanwhile, lives in an anonymous flat on the Oxford ring road, all but ignored by the global aid industry. As Wrong gloomily concludes, for an African dissident “being proved right is never enough”.

It's Our Turn to Eat by Michela Wrong
Fourth Estate £12.99 pp368

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