Something must be done! Something really must be done about Zimbabwe - and Thabo Mbeki should do it. The call gets louder, the logic gets weaker.

Those who urge the South African president to act are like Pooh Bear and his hums. They believe if they sing the first line often enough and fast enough - "Something must be done" - the next lines will come automatically. The device did not succeed with Pooh; nor is it working for Mr Mbeki's critics.

What, precisely, should the president be doing? Imposing trade sanctions? Hardly. Zimbabwe is already enduring Mr Mugabe's devastation of commercial agriculture. It is being hit by the sanctions of the market place. Investors and holidaymakers are staying away. Tourism, one of the main foreign exchange earners, has collapsed; the currency has plummeted; inflation has rocketed.

Do we expect South Africa to impose a fuel embargo? Or hold up the railway wagons on landlocked Zimbabwe's trade route through South Africa? Prime Minister Vorster used that tactic to put the squeeze on white ruled Rhodesia in the 1970s. It may be tempting. But the danger is that such action could well precipitate an even deeper crisis. And Mr Mugabe's irrationality and unpredictability - and his sheer brutality - are among his most potent weapons.

Should Mr Mbeki intervene militarily? Before we urge him down that path, let's recall history. Tanzania's military invasion of Uganda to oust Idi Amin was a disaster. True, the invaders forced Amin to flee. But they left behind towns devastated by the fighting with retreating Ugandan forces. And the country's former Prime Minister, Milton Obote - buddy of Tanzania's Julius Nyerere – regained power in an ill-organised and disputed election - albeit approved as free and fair by the Commonwealth observers. Only when the despotic Obote was overthrown in 1986 did Uganda begin to recover from the combination of Amin and the invasion.

The suggestion that Mbeki is reluctant to act because Mugabe is an old comrade of the liberation struggle does not square with the facts. The South African guerrillas were in an alliance with the army of Joshua Nkomo, bitter rival of Mugabe. Far from treating Mugabe's men as allies, they were often seen as enemies. For some members of the post-apartheid South African army, there may be scores to settle.

So why does Mr Mbeki not, at the very least, denounce Mugabe and the suffering he has caused? Why does he not give him the cold shoulder at diplomatic functions? Why does he not condemn the elections as a sham?

But then what? None of these actions will faze Mr Mugabe, or loosen his hold on power. So what can be done?

* Prepare and publish an emergency recovery programme which may help stiffen resistance to tyranny. It would tabled without delay, to be implemented when Zimbabwe begins a return to democracy; and would be funded by donors, and provide the essentials - basic medicines, agricultural inputs, school books.

* Spend part of the £30m that Britain's aid agency, Difid, has earmarked for land reform, resettling commercial farmers and their senior staff in neighbouring Mozambique.

* Name and shame the banks that continue to lend to Zimbabwe. This tactic forced Barclays to withdraw from white-ruled South Africa - it can do the same in Zimbabwe.

* Commission and publish an independent evaluation of the regional consequences of a real collapse in Zimbabwe. It might concentrate the minds of African leaders.

* Attach conditions to food aid. But don't hold your breath. An opportunity to put pressure on Mr Mugabe first came in November 2001, when the UN World Food Programme unilaterally announced its intention to feed Zimbabwe. A chance was missed. The WFP should have consulted the donor governments about the terms. It did not. And instead of making food aid conditional on electoral reform, supplies were distributed without obligation.

Times Recommends

• Lies and cover-up at MG Rover exposed by report
• High oil prices push manufacturing costs up
• Primark founder steps down as chief executive