Regulators have agreed in principle to allow human-animal embryos to be created and used for research.

But scientists wanting to use hybrids will still need to make individual applications, the Human Fertilisation and Embryology Authority said.

An HFEA consultation showed the public were "at ease" with the idea when told it could pave the way for therapies for conditions such as Alzheimer's disease.

Opponents have said many people would be "horrified" by such a move.

Scientists want to create hybrid embryos by merging human cells with animal eggs in a bid to extract stem cells. The embryos would then be destroyed within 14 days.

The cells form the basic building blocks of the body and have the potential to become any tissue, making them essential for research.

At the moment, scientists have to rely on human eggs left over from fertility treatment, but they are in short supply and are not always good quality.

Two teams from Kings College London and Newcastle University have already applied to the HFEA to use hybrid embryos.

It is now expected individual hearings for these two applications will be held in November with other scientists expected to follow suit.

Dr Stephen Minger, of King's College London, said he "applauded" the HFEA for its decision as it was the only ethically justifiable option if scientists were to push forward with their research.

Lyle Armstrong, of Newcastle University, added: "This is excellent news. It is a positive outcome not just for our work but for the progress of British science in general and we hope that this will lead to new technologies to benefit everyone."

And he also said: "It does seem a little abhorrent at first analysis, but you have to understand we are using very, very little information from the cow in order to do this reprogramming idea.

"It's not our intention to create any bizarre cow-human hybrid, we want to use those cells to understand how to make human stem cells better."

Lib Dem MP Dr Evan Harris, a member of the Commons' science and technology committee, which has already given its backing to such research, said: "Our top-class researchers can now proceed with their applications to conduct this world-leading research."

The HFEA decision comes amid government moves to lay down regulations covering such research - the law governing embryo research is out of date and does not cover the issue.

The government originally proposed banning the technique in a white paper last year.

But it reversed its decision this year in a bill which indicated ministers were minded to allow hybrid embryos which were 99.9 per cent human and 0.1 per cent animal, following a backlash by scientists and patient groups.

But the HFEA has carried out its own review ahead of parliament passing the legislation so as not to hold back research.

The regulator can grant licences to scientists to pursue such research, but will have to change its criteria if future rules contradicted its own practices.

Dr Helen Watt, from the Linacre Centre for Healthcare Ethics, said the technique was "a further violation of the rights of the embryo".

"The embryo is deprived not only of its life in the course of the experiment, but of any human parents.

It is further dehumanised by the very method of its creation."

And Josephine Quintavalle, of the campaign group Comment on Reproductive Ethics, said the HFEA was wrong to be pushing ahead with a decision which should be left to parliament.

"Using hybrid embryos has never been acceptable - it offends the dignity of humans and animals."

A spokeswoman for the HFEA said the decision had been a challenging one to reach.

"This is not a total green light for hybrid research, but recognition that this area of research can, with caution and careful scrutiny, be permitt