In experiments that mirror the cloning technique used to make Dolly the sheep, they took cells from men’s arms and legs and placed them into women’s eggs.

The embryos created lived for only five or six days, but they represent a key step in the quest for treatments for incurable diseases from Alzheimer’s to cancer.

Very early-stage embryos have been made from human skin before but the researchers claim to have got further than anyone else.

Importantly, according to the journal Nature, they appear to have worked out why others have failed – meaning the research could now progress in leaps and bounds. The scientists, from the New York Stem Cell Foundation Laboratory, paid 16 young women for their eggs and took tiny samples from the skin of two men.