Human organs could soon be grown inside animals for the first time after Japan gave permission for scientists to begin controversial experiments.

The technique involves genetically modifying sheep or pig embryos so they cannot grow a specific organ. Human stem cells are then injected into the embryo in the hope that the DNA will fill in the missing code.

The hybrid embryos would then be implanted back into the original animal or a surrogate, and the baby animal would be born with a human organ.

If successful, it could mean an unlimited supply of organs for transplants or even a cure for Type 1 diabetes, if an entirely new pancreas could be created.