Cambridge University mixed two kinds of mouse stem cells and placed them on a 3D scaffold. After four days of growth in a tank of chemicals designed to mimic conditions inside the womb, the cells formed the structure of a living mouse embryo.

The breakthrough has been described as a 'masterpiece' in bioengineering, which could eventually allow scientists to grow artificial human embryos in the lab without the need for a sperm or an egg.

Growing embryos would help researchers to study the very early stages of human life so they could understand why so many pregnancies fail, but is likely to prove controversial and raise ethical questions about what constitutes human life.

urrently scientists can carry out experiments on leftover embryos from IVF treatments, but they are in short supply and must be destroyed after 14 days. Scientists say that being able to create unlimited numbers of artificial embryos in the lab could speed up research while potentially removing some of the ethical boundaries.