Zimbabwe may be on its knees economically, while a cholera epidemic claims more than 1,000 lives, but Robert Mugabe's grip on power is unshaken. To date a dozen countries, including Britain, America and France, have called for his removal, but the 84-year-old ruler has not budged. In a speech to his supporters at the ruling Zanu (PF) annual conference, Mr Mugabe mocked his adversaries. African nations were “not brave enough” to topple him, Britain would never win its battle against him - “Zimbabwe is mine,” he declared.

It is hard to challenge his assertion. Nine months ago Mr Mugabe and his Zanu (PF) thugs used violence and intimidation to reverse the results of an election victory for the opposition Movement for Democratic Change (MDC). The world was suitably outraged. Gordon Brown and Lord Malloch-Brown, the Foreign Office Minister responsible for Africa, pushed for action at the United Nations, confident that quiet diplomacy combined with Zimbabwe's isolation would bring the regime to its knees. Mr Mugabe had “at most, weeks or months left in office”, they predicted.

How wrong they were. Russia and China blocked any hope of concerted UN action. America became distracted with other pressing problems at home and abroad. South Africa devised a power-sharing agreement intended to leave Mr Mugabe in power. Britain, we now learn, was long on talk but short on action. While Whitehall stepped up the rhetoric, it turned a blind eye to British-based businesses that helped to prop up the regime in Harare.

So how much longer must this tragedy continue? Until Zimbabwe's neighbours are forced to act out of self-interest when millions of desperate refugees, some infected with cholera, pour across their borders? Until Mr Mugabe dies peacefully in his palace? Until one of his cronies decides to seize power for himself?

Times Archive, 1983: And now the real Mugabe stands up

His elegance of speech, and gentleness of manner, have deceived many in the West

• Leading article: Zimbabwe's vote, 1985

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If the world is serious about defending human rights and democracy and encouraging development and good governance in Africa, then there are real opportunities at hand. In less than a month Barack Obama will be sworn in as US President. There are many demands being made of him, but he must be urged at the highest level to act immediately on Zimbabwe.

As a half-African whose grandfather was part of the liberation movement against the British in Kenya, he needs no lectures about neo-imperialism from the likes of Mr Mugabe. There is huge support for Mr Obama on the continent; some of the more courageous countries, such as Kenya, Zambia and Botswana, have already broken ranks to condemn Zimbabwe and demand change.

Mr Obama must galvanise this movement. Above all, he must use all the considerable weight of his office to pressure South Africa, the critical power in the region, to stop shielding Mr Mugabe. Jacob Zuma, the new ANC leader and South Africa's likely next President, must be told in unambiguous terms that removing Mr Mugabe must be his top priority. If not, South Africa's relations with America and Europe will be set back at every level, from aid to trade and even the football World Cup Final in 2010.

For too long Thabo Mbeki, the former South African President, was allowed a seat at the top table of international affairs while neglecting his primary responsibility to the wellbeing of his neighbours in Zimbabwe.

If force is needed - for instance, to protect humanitarian relief efforts to rescue millions from disease and hunger - then South Africa must be ready to weigh in, as it did in other African emergencies. America and Britain must be ready to assist any African-led operation with logistics and money.

The slow death of Zimbabwe has dragged on for the best part of a decade. The country is still salvageable, but not if Mr Mugabe is still around in 2010.

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