As he drives out into the dusty fields of Kandahar province keeping one eye open for the Taleban, Harry Spies can't help daydreaming sometimes about the farm he used to have in Zimbabwe.

Three years after he gave up on Africa, Mr Spies is one of a number of white farmers who have brought their knowledge of agriculture, and experience of guerrilla warfare, to the opium fields of southern Afghanistan.

A handful of contractors are almost the only foreigners still risking commercial work in the south. Veterans of the 1970s bush war are prominent among them. They use their skills to set up agricultural projects which provide an alternative to opium for farmers.

In Zimbabwe, Mr Spies was one of the lucky ones. He leased his farm, finally giving up in 2005 when he decided the writing was on the wall. A fellow ex-Zimbabwean who works alongside him in Afghanistan had paid the final instalment on his property a week before it was invaded by Robert Mugabe's “war veterans”.

From Kandahar and Helmand, all of them have been keenly watching events back home. Mr Spies believes that even if Mr Mugabe leaves power the farmers who left can never go back to their old life in Zimbabwe.

He said: “You put your heart and soul into those farms. They were your retirement - they were something to pass on. Your labour force was like an extended family which you fed and educated.

“That's gone now. Farmers would only go back if the World Bank or somebody like that would give guarantees, and now a farm would have to be run as a commercial enterprise like a factory or a business.”

Unlike some farmers, Mr Spies is not entirely resentful of Mr Mugabe and believes that his reforms helped those farm labourers who were not lucky enough to have good employers.

In the last few years about 1,200 white farmers out of 4,500 have given up on Zimbabwe and moved abroad, crippling the rural economy. Most have gone elsewhere in Africa or to Australia and New Zealand.

An American entrepreneur working on agricultural projects for international aid agencies such as USAid first recognised their value in the uniquely difficult farming environment of southern Afghanistan.

[]Steve Shaulis, the owner of Central Asia Development Group, said: “Our Zimbabwean staff are among the best farmers in the world and have the toughness to operate in the unforgiving environment of southern Afghanistan. They are comfortable with providing their own security in the field.”

The CADG farmers have helped Afghan villagers establish modern drip feed irrigation systems to replace traditional irrigation which was destroyed by the Red Army, as well as running cash-for-work programmes to give labourers an alternative to opium harvesting.

Although it works in the most difficult provinces in the country the company has had no serious security incidents with its workforce. In contrast to the giant corporations who only venture out in armoured cars with large numbers of armed guards it works close to the community, receiving the protection of tribal leaders in return.

Years of war and destruction have impoverished Afghan farmers and left them addicted to opium as a cash crop, but the Zimbabwean farmers believe agriculture could have a bright future in southern Afghanistan once roads and electricity are developed.

Mr Spies said: “The quality of the fruit is very good - fantastic pomegranates, almonds and grapes. Farmers don't make that much cash out of opium and when they grow it they are preyed on by some nasty moneylenders. They would switch to orchard crops, which make almost as much money, if there was an infrastructure for getting them to market.”

Their own army experience may have been decades ago but it is still invaluable. “If you really fall in the cactus you know what to do,” Mr Spies said.

Some have never really got over it. “What is this Zimbabwe?” fumed one of his colleagues when The Times asked about his past. “I am a Rhodesian.”

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