A major shift of position by ministers has cleared the way for scientists to create hybrid animal-human embryos for stem cell research.
The move followed a White Paper proposal banning the hybrids that attracted criticism from scientists, charities, patient groups and MPs.
The Government published a draft Bill that effectively sweeps away the ban, but Health Minister Caroline Flint, its chief architect, denied talk of a climbdown.
Under the Human Tissue and Embryos Bill, scientists will be allowed to produce "cytoplasmic" hybrid embryos that are 99.9% human and 0.1% animal.
The Bill goes further and permits human embryos to be altered by the introduction of animal DNA.
Ms Flint said that while recommending a "general prohibition", the White Paper had always left the door open for specific research to be allowed on a case-by-case basis. But the immediate ban called for by the White Paper has now been removed.
The Bill also allows human-animal chimeras - human embryos that have been physically mixed with one or more animal cells. True animal-animal hybrids, creatures "bred" by the fusion of sperm and eggs, remain outlawed.
In all cases it would be illegal to allow embryos to grow for more than 14 days or be implanted into a womb.
Technically, the Bill faces a further hurdle in the form of a pre-legislative scrutiny committee before being finalised. However, this is mainly to resolve technical issues and is not likely to result in any significant changes.
Speaking at a briefing at the Department of Health in London, Ms Flint said the debate had moved on in the last few months, making the scientific issues clearer. She said: "I honestly don't see this as a back flip ... it was an evaluation of a number of different view points. Our position was not to stop this research but to be clear that it's sensitive research, and we have to be sure about what we're going to permit to happen in the future. The position was a general prohibition, but with the opportunity on a case-by-case basis for certain types of research to take place".
