A crop spray which can boost farmer's wheat yields by one fifth, without the need for genetic modification, has been developed by scientists at Oxford University.

Researchers have found a molecule which helps plants make the best use of the sugary fuel that they generate during photosynthesis. And with more fuel, the plants can produce bigger grains.

Other scientists in Britain have developed ways to genetically modify crops to increase yields, and the Department of Environment is currently deciding whether to allow a field trial for GM wheat in Hertfordshire.

But genetic modification has proved controversial with campaigners warning it could disrupt nature or be toxic to humans, while critics point out that GM has never been proven to increase yields, despite 20 years of trials.

In contrast, the new technique which is described in the journal Nature, would be far less controversial, and could be administered simply by farmers using a crop-sprayer. The results were seen after just one application.