The reverse brain drain of researchers leaving the United States looks set to gather pace after the House of Representatives voted this week to ban all cloning of human embryos.
The congressmen passed the bill on Tuesday night, by 265 to 162. An amendment to allow limited cloning for stem-cell research into cures for disease was defeated by 249 to 178.
Patrick Bateson, biological secretary and vice-president of the Royal Society, said: "This is a disaster for research in the States. It will be good for the UK but the decision was based on moral confusion."
Peter Andrews, a pioneer of stem-cell research at Sheffield University, said that in the short term the ban would have little impact as the most pressing research is in understanding the biology of stem cells. But he said that later on, the ban would prevent treatments where patients' own cells were used to grow replacement tissue, lowering the risk of immune rejection.
He said that the United Kingdom's clear legal framework put it in a strong position and may attract US researchers.
Robin Lovell-Badge, head of developmental genetics at the National Institute of Medical Research in London, said: "The problems to solve in getting reproductive cloning to work are enormous and very different from those of therapeutic cloning."
President George W. Bush supported the vote. He said: "We must advance the promise and cause of science, but must do so in a way that honours and respects life."
But the bill may yet fail to become law as it has to be passed by the Democrat-led Senate, which is thought to be more sympathetic to stem-cell research.
The climate for stem-cell research in the US has become increasingly hostile. Federal funds cannot be used to create embryo stem-cell lines, which usually come from spare in-vitro fertilisation embryos. President Bush is considering whether to lift the ban on federal funding for research using stem-cell lines that have been derived already.
Britain is the only country with legislation allowing cloning for therapeutic purposes. Most countries have imposed a ban or have yet to legislate.
Last month, Californian researcher Roger Pedersen announced he was moving to the UK to continue his work "with public support". Stem-cell research has been prioritised by the Medical Research Council, which said that it would be "pleased if highly qualified people wanted to contribute to this research".
Jonathan Grant, head of policy at the Wellcome Trust, said: "Britain's approach has been to take the responsible pro-science stance. We have actively promoted therapeutic cloning, which has the potential to save the lives of many... but prevented any work on reproductive cloning."