But the Human Fertilisation and Embryology Authority (HFEA), a regulatory body that oversees embryo research and fertility treatment, is expected to turn down applications from three research groups next week to carry out this type of work.

"Informally, we have been told that our applications are unlikely to be granted," Professor Stephen Minger of the Stem Cell Biology Laboratory at Kings College told reporters.

"Britain leads the world in stem cell research and for the government to back off on a very reputable, regulatable area of research, which has so much potential value, seems to be really short-sighted," he said.

Minger and colleagues want to harvest stem cells from hybrid embryos that would be created by inserting human DNA into a hollowed out cow or rabbit egg, from which the nucleus has been removed.

Such embryos would be more than 99 percent human but would still contain a small amount of animal DNA found in mitochondria -- cellular power plants outside the nucleus.

The idea is to grow the embryos to only a very early stage and then generate stem cell lines from them that are capable of developing into many different cell types for research.

This would allow scientists, for example, to study motor neurones from people with motor neurone disease in the laboratory for the first time.

The embryos themselves would be destroyed within 14 days.

"To us, it's a logical step to use animal eggs and preserve human eggs, which are in short supply," Dr Lyle Armstrong the North East England Stem Cell Institute said.

Scientists in China, the United States and Canada have already carried out similar work. However, a British government White Paper last month proposed banning it.

Dr Evan Harris, a Liberal Democrat member of parliament, said a ban would be wrong-headed.

"What would be unethical would be for hybrid embryos to be given greater protection than human embryos, which can be created and used for up to 14 days before being destroyed, and for patients to be denied the chance to benefit from research just because some people find it distasteful," he said.