Daniel Howden: Sad day for Africa as high flier walks away

Speaking in Abuja only three months ago, Ngozi Okonjo-Iweala identified her greatest achievement, and without knowing it, the seed of her own downfall.

"People in power now know they can't act with impunity," she told The Independent. A few weeks after making this pronouncement she was shuffled out of the finance ministry, while holding on to control of the economic reform panel. Then she was stripped of that role too, and has responded by walking away from the government.

The international community can look too hard for heroes in Africa and has an exaggerated tendency to find them among outsiders like Mrs Okonjo-Iweala who come into government with a proven record in international institutions. But the former World Bank executive offered a genuine reason for optimism in a country racked by corruption, sectarian divisions and an oil-fuelled insurgency in the Niger Delta.

Like her fellow economist, Ellen Johnson-Sirleaf, who became Africa's first female president when she won elections this year in Liberia, Mrs Okonjo-Iweala is part of a vanguard of highly educated and well-paid African professionals who have returned home to take office.

The scale of the problems facing reformers both in conflict-shattered Liberia and in chronically corrupt Nigeria is immense. An activist working in the oil-rich and violent Niger Delta was unequivocal over the extent of the graft in what should be the economic powerhouse of Africa. "Nigeria is run on corruption," he said. "It is the only thing holding the country together."

If you walk into any government ministry you will be asked for bribes. Police on the streets will ask for bribes. Unpaid civil servants rely on bribes to survive.

In this context it is unrealistic to expect one person to effect change. Another student of economics who later became a campaigning journalist, John Githongo, quickly encountered the limits of his role as anti-corruption czar in Kenya last year when he switched from running an NGO to playing a part in government. He walked out on the administration of President Mwai Kibaki, accusing senior ministers of "massive looting", only three years after being elected on a ticket of cleaning up Kenya.

Governments in pursuit of international debt relief who are keen to appear busy on the issue of corruption are fond of appointing their critics. More often than not this has been a case of window-dressing rather than reform.

Nigeria's President Olusegun Obasanjo has been making the required noises about reform for years with little end product in sight. Until this week there was the slim hope that Mrs Okonjo-Iweala was making progress. That's now gone.

No one yet knows whether the World Bank veteran has looked at Liberia and decided that her home country needs a female president. With elections due next spring and Mr Obasanjo barred from running again, Mrs Okonjo-Iweala may have stepped back to prepare for a run at the highest office. There will be many Nigerians, at home and abroad, hoping that this is not the end of her political career.