Scientists have harnessed knowledge they have had since the 1960s - that crops with smaller stems produce more plants.

Research at the John Innes Centre in Norwich has pinpointed the genetic formula for producing dwarf varieties of wheat. Its spokesman, Dr Ray Matthias, said there are "potential benefits for developing countries".

The new discovery puts less of the plant's resources into growing straw and more into developing grain, with the dwarf gene being added in the laboratory.

Dr Matthias said the gene had been used in plant breeding for wheat for years.

"What's new is that for the first time we have actually been able to purify the gene and isolate it," he said.

The gene could work for a variety of crops, not just wheat

"The important point is that we expect that dwarf forms of rice will actually produce higher yields."

He said that because of the way the gene works, it will be effective in plants other than wheat and rice. He cited oil seed rape as a possibility.

But the findings were not welcomed by Andrew Simms of Christian Aid. He said they were a "genetic roulette", and that there was no guarantee it would help developing countries, or that they would get a "fair deal".

Prime Minister Tony Blair hit the headlines recently when he said the media was giving huge space to "anything which fed the hysteria" over genetically-modified (GM) foods.

He told colleagues that positive scientific reports were barely reported.