Kampala — Phumzile Mlambo-Ngcuka, South Africa's recently appointed deputy president, has a sense of humour, so maybe she was just joking. But it was the political equivalent of shouting "Fire" in a crowded theatre, and it has severely shaken confidence in the good sense of the government she helps to lead.

What she said at a conference in Johannesburg last week, was the following: "Land reform in South Africa has been too slow and too structured. There needs to be a bit of "oomph". That's why we may need the skills of Zimbabwe to help us. On agrarian and land reform, South Africa should learn some lessons from Zimbabwe, how to do it fast."

As investors hit the panic button and the people who run South Africa's economy tore their hair out in despair, Mlambo-Ngcuka's spokesman, Murphy Morobe, insisted that her remarks were made in jest during a "light-hearted exchange" during the conference. Perhaps. But if not, then she was suggesting that South Africa destroys its agriculture, and subsequently its economy, by emulating Zimbabwe

Zimbabwe was, until the end of the 1990s, a repressive but modestly prosperous country ruled by an ageing leader of the independence struggle, Robert Mugabe. It was only after voters rejected his plan to make the country a one-party state (and thereby assure him the presidency for life) in a 2000 referendum that he turned to extreme measures in an attempt to rebuild his popularity.

Primary among them, and a sure crowd pleaser, was a plan to confiscate land from prosperous white commercial farmers and "redistribute" it to poor, landless blacks.

It was indefensible that a few thousand white farmers owned most of Zimbabwe's best farmland. Land reform was long overdue, and if Mugabe had set about it seriously 20 years earlier, when he first took power, it could have been done gradually, legally, and without any grave damage to the economy.

But it was bound to be a delicate operation, because the white farmers grew the cash crops that were the mainstay of Zimbabwe's economy, and the landless blacks, who took over their farms, would initially lack the skills and the capital to fill that role.

Mugabe may not have understood that, and in any case, he didn't care. This was about politics, not the economy, and so he sent out gangs of armed youth to expel the white farmers and seize the land. Almost all the white farmers are now out of business, and so is Zimbabwe.

About half of the seized land went to Mugabe's political allies in the ruling party and the military. Some did go to poor peasants, but they had neither the tools nor the skills for large-scale commercial farming, and about half of the best farmland now lies fallow.

The national economy has shrunk by 30% since 1999, average income per head is now lower than in 1980, and half of the population now needs emergency food aid. Is this what deputy president Phumzile Mlambo-Ngcuka has in mind for South Africa?

The ANC government has been walking a tightrope ever since it took control of South Africa 11 years ago. Most black South Africans still vote for it, but they expect rapid action to narrow the shocking gap between their living standards and those of the non-black minorities. The trouble is that those minorities - whites, Asians, and mixed-race "Coloureds" who together account for only one-fifth of the country's 45 million people, still own most of the businesses, and possess most of the skills, that South Africa needs if it is to remain a modern industrial economy.

This must change in time, of course, but change can only be gradual if the economy is not to be destroyed. The pressure for change is urgent, however, and only politics can span the gap. The ANC has walked the political tightrope successfully for a decade, but at least another decade of the same performance lies ahead of it if South Africa is to make it into stable prosperity as a multi-racial democracy.

Occasionally, the leadership panics and decides a populist gesture is necessary, and that is the charitable explanation for Mlambo-Ngcuka's remarks. Eighty-seven percent of South Africa's farmland was white-owned when Nelson Mandela took over in 1994; 85% still is today. So late last month, the government announced it was abandoning the market-based "willing buyer-willing seller" programme of land redistribution because it is too slow.

White farmers say there are plenty of "willing sellers", but that they cannot get the government to buy their land. It doesn't matter who is right. It doesn't even matter all that much if a "fast-track" programme of taking land from whites and handing it to blacks destroys South Africa's position as one of only six net food exporters in the world.

Unlike Zimbabwe, South Africa is a mostly urban country with a fully developed economy, and agriculture is not a very big part of it. What does matter is that both South African and foreign investors continue to see the country as a place where it is the law, and not mere party politics, that makes the rules. Get that wrong, and you lose everything. She really should mind her mouth.