Scientists in Norwich have applied for official permission to plant GM potatoes in a field trial at Colney.

The three-year trial involves two plots of Desiree potatoes that have been genetically modified by scientists from the Sainsbury Laboratory at the John Innes Centre, part of Norwich Research Park.

The potatoes will be planted from early May, if approved, and have been modified with resistance to late potato blight, which can devastate commercial crops and led to the death from starvation of about two million people in the 19th-century Irish Potato Famine.

Prof Jonathan Jones, group leader at the Sainsbury Laboratory, said the trials have to be conducted outside to assess effectiveness against late blight, which costs farmers an estimated £3.5bn worldwide each year. And routine fungicide spraying, up to 17 times in a typical growing season to protect crops in Britain from the increasingly-aggressive types of blight, is also costly.

Over three years, the trials will cover 1,000sq metres of land owned by the John Innes Foundation. They will be grown inside a guard or protective crop of conventional Maris Piper potatoes.

The GM potatoes would not enter the food chain, but would be destroyed after analytical tests.

Prof Jones said: "We've taken late blight resistant genes from wild relatives of potato. We're going to put them into the field to see if they're still resistant."

The two plots of about 50 plants each have a different GM line and with the "nurse" crop cover a total of 200sq m or about two-thirds of a typical allotment.

The land, which is surrounded by a high fence, will not be cropped for two years after the trials have been completed.

"There is no scientifically credible reason whereby any such experiment can damage the environment or human health. A lot of public money has gone into isolating these genes," said Prof Jones.

GM potato trials have taken place at Cambridge and also at Leeds for agro-chemical company, BASF.

Cambridge-based Dr Tina Barsby, chief executive of the not-for-profit National Institute of Agricultural Botany, said the trials had produced a tremendous response.

"The difference between the GM potatoes and the conventional control was like night and day. There was a quite severe attack of blight and the leaf cover of non-GM potatoes was destroyed while the others were still green and lush and protected with no sprays," she said.

Dr Barsby, who carried out small-scale GM potato trials at Terrington, near King's Lynn, more than 10 years ago, said that it could take at least five to 10 years for these blight resistant potatoes to be commercially available.

She said NIAB, which evaluates plants for Defra, had found that crosses of wild potatoes with some resistance, had not been as effective as the results of the GM potato trials.

Norfolk crop adviser John Purselow, said the blight sprays sometimes had to be applied every four days and up to 17 times. It could cost from £200 an acre or almost a tenth of the cost of growing a potato crop, he added.