By Clare Murphy
BBC News health reporter
It sparked impassioned debate, but less than a year after parliament refused to ban hybrid human animal embryos scientists say a lack of funding means their research has been put on ice.
Scientists at Newcastle University hold one of the hybrid licenses
Condemned as "Frankenstein" science by at least one religious leader, and rejected by the majority of the Tory shadow cabinet, hybrids proved one of the most controversial aspects of the Human Fertilisation and Embryology Bill.
But since the bid to outlaw the research was defeated in May last year, two of the three groups which hold a license to create hybrid embryos have been unable to find funding, while the third has yet to try.
Human animal hybrid embryos - in which the nuclei of human cells are inserted into animal eggs - have been seen as one of the most promising ways of overcoming the dramatic shortage of good quality human eggs.
The stem cells then extracted from the embryos - which are some 99% human and 0.1% animal - have the potential to become any kind of tissue and as such could be used to develop treatments for cancer and conditions like Parkinson's and Alzheimer's disease.
"We can't do anything at the moment, we just don't have the money" says Dr Stephen Minger, of King's College London, who received his license over a year ago.
"What we have to work out now is whether it's a good use of our scant resources to put our efforts into resubmitting a proposal - which is incredibly time-consuming."
Dr Lyle Armstrong, of Newcastle University, who has failed to find money to take his hybrid research to a next stage added that "legislation does not guarantee that funding will follow".
End of the line?
The Medical Research Council, one of the principal funding sources for UK scientists, rejected any suggestion that moral reservations meant projects were being rejected.
It stresses that only one in five applications are ultimately approved after a lengthy and rigorous review process in which rejections by one scientific panel are reviewed by another.
The MRC's chief executive, Sir Leszek Borysiewicz, said the council had been instrumental in ensuring that hybrid embryos research was included in last year's bill.
"Clearly, we believe there may well be great potential for this avenue of research," he said, but added: "Fighting for the right to carry out such research does not mean that it should get priority over other applications which score higher and hold more promise."
The Biotechnology and Biological Sciences Research Council, another leading funding body, said it too had received applications for this kind of research which had been rejected.
Colin Miles of the BBRSC stressed that "the competition for funding is very high indeed and many very good applications don't get funded purely and simply because the pot of money available is finite."
Science has also continued to move on since last year's heated debate.
Induced pluripotent stem cells (IPS) are adult stem cells which are made to act like embryonic ones with the ability to become any cell in the human body.
They too have the potential to be used to treat a range of degenerative conditions and also circumvent the need to use human eggs or destroy embryos - although scientists involved admit therapies could still be many years away.
"There has been a lot of movement on this front and this probably has caused the scientific community to reflect a bit - technologies move on very rapidly," says Chris Mason, professor of Regenerative Medicine Bioprocessing at University College London and a member of the UK National Stem Cell Network.
"But none of this is mutually exclusive and there is still definitely a role for hybrid research. I simply do not believe that moral reservations are at play - the right proposal will always find the money."
Professor Justin St John, who holds the third license, said he had no reason to believe that his proposal for human-pig hybrids would not recieve a fair hearing.
"There are a number of promising avenues but a lot of what we learn from IPS is transferrable to hybrids and vice-versa - we have to keep investigating everything and at some point in the future all these strands will hopefully come together.
"In the end it comes down to the best science, and if we demonstrate that we are onto something then I think we are in with a good chance."