Scientists have begun putting genes from human beings into food crops in a dramatic extension of genetic modification. The move, which is causing disgust and revulsion among critics, is bound to strengthen accusations that GM technology is creating "Frankenstein foods" and drive the controversy surrounding it to new heights.

Even before this development, many people, including Prince Charles, have opposed the technology on the grounds that it is playing God by creating unnatural combinations of living things.

Environmentalists say that no one will want to eat the partially human-derived food because it will smack of cannibalism.

But supporters say that the controversial new departure presents no ethical problems and could bring environmental benefits.

In the first modification of its kind, Japanese researchers have inserted a gene from the human liver into rice to enable it to digest pesticides and industrial chemicals. The gene makes an enzyme, code-named CPY2B6, which is particularly good at breaking down harmful chemicals in the body.

Present GM crops are modified with genes from bacteria to make them tolerate herbicides, so that they are not harmed when fields are sprayed to kill weeds. But most of them are only able to deal with a single herbicide, which means that it has to be used over and over again, allowing weeds to build up resistance to it.

But the researchers at the National Institute of Agrobiological Sciences in Tsukuba, north of Tokyo, have found that adding the human touch gave the rice immunity to 13 different herbicides. This would mean that weeds could be kept down by constantly changing the chemicals used.

Supporting scientists say that the gene could also help to beat pollution.

Professor Richard Meilan of Purdue University in Indiana, who has worked with a similar gene from rabbits, says that plants modified with it could "clean up toxins" from contaminated land. They might even destroy them so effectively that crops grown on the polluted soil could be fit to eat.

But he and other scientists caution that if the gene were to escape to wild relatives of the rice it could create particularly vicious superweeds that were resistant to a wide range of herbicides.

He adds: "I do not have any ethical issue with using human genes to engineer plants", dismissing talk of "Frankenstein foods" as "rubbish". He believes that that European opposition to GM crops and food is fuelled by agricultural protectionism.

But Sue Mayer, director of GeneWatch UK, said yesterday: "I don't think that anyone will want to buy this rice. People have already expressed disgust about using human genes, and already feel that their concerns are being ignored by the biotech industry. This will just undermine their confidence even more."

Pete Riley, director of the anti-GM pressure group Five Year Freeze, said: "I am not surprised by this.

"The industry is capable of anything and this development certainly smacks of Frankenstein."