The spectre of a human clone

International calls for new laws to prevent the cloning of humans are growing as the full implications of the cloning of a sheep by scientists in Edinburgh begin to dawn.

Some scientists even compared the possible effects on humanity to that of the atomic bomb, while US President, Bill Clinton, said the cloning of Dolly the sheep raised "serious ethical questions, particularly with respect to the possible use of this technology to clone human embryos". He told a panel of bioethics experts to report back to him in 90 days on the ethical and legal implications of the Edinburgh work.

Since the news first emerged on Sunday, the cloning breakthrough has enthralled the US. That same day the story led the New York Times, the country's most prestigious newspaper. It has dominated television news, provoked weighty leading articles and provided endless grist for the talkshows.

The fascination partly reflects an obsession with scientific and medical news in a country where tenuous results from routine health studies make front-page headlines. But it is also a measure of the ethical and legal conundrums raised by the possible cloning of humans. In France Philippe Vasseur, the farm minister, raised the bizarre spectre of "six-legged chickens" and promised stiff new controls if the technology led to "monstrous" experiments with nature.

More material benefits of the work showed up in a booming share price for PPL Therapeutics, which carried out the work with scientists at the Roslin Institute in Edinburgh. PPL's shares have risen by more than one- third since Monday morning, increasing its market value by pounds 25m.

However, the Roslin scientists own no shares in the company, and will not benefit directly from their breakthrough. The cloning technology has been patented jointly by PPL and the Institute, though that might not prevent a determined - and very wealthy - person from spending millions of pounds to put together a cloning laboratory for their personal immortalisation.

The UK, Spain, Germany, Canada and Denmark have laws against cloning humans, as do some individual states in the US. France and Portugal also have very restrictive laws on the use of cloning. But many countries do not. That has raised the possibility that the publication tomorrow in Nature, the scientific journal, of the technique involved in using a cell from an adult sheep to produce Dolly could be used to clone people.

Professor Martin Johnson, of the Human Fertilisation and Embryology Authority, said yesterday: "The important thing isn't to raise fears about what might go on [in the UK], but elsewhere. There's a general consensus that cloning people would be negative, but the legal framework isn't unified." In the US, for example, federal funds cannot be used to fund research on human embryos. But the position is unclear for privately funded science.

Joseph Rotblat, the British physicist who won the Nobel Peace Prize in 1995 after battling for years against nuclear weapons, said: "My worry is that other advances in science may result in other means of mass destruction, maybe more readily available even than nuclear weapons. Genetic engineering is quite a possible area, because of these dreadful developments that are taking place."

It is still uncertain whether it would be possible to clone a human from an adult cell. Dolly was produced by taking a cell from an adult sheep and putting it into a "genetic coma". The nucleus and DNA of that cell were then put into an unfertilised egg from which the DNA had been removed, and the resultant cell implanted into a ewe.

In theory the same principle might work in humans. But it has failed in frogs and mice, because it is more difficult to put their cells into the required form of genetic coma. Scientists instead now want to try the technique on pigs and cows.

Professor Grahame Bulfield, director of the Roslin Institute, insisted yesterday that they would not allow cloning to be used in harmful ways, and especially not for work on humans. Instead, he said, the breakthrough could in the long term lead to a myriad of new ways to help humans. Herds of transgenic animals could be farmed for proteins, blood and organs. Gene therapy, with its ability to replace faulty genes with good ones, could provide cures for fatal diseases

It could take years for the technology to be proven and field-tested sufficiently to be licensed. But after that it could be worth millions of pounds annually, with a huge number of applications.