Although studies are just beginning the scientists have already made new findings including the fact that embryos create two cavities to grow in, one for the foetus and one for the placenta.

Dr Simon Fishel, founder and President of CARE Fertility Group, adds: “This is about much more than just understanding the biology of implantation embryo development. Knowledge of these processes could help improve the chances of success of IVF, of which only around one in four attempts are successful.”

Currently UK law bans laboratories for growing embryos for longer than 14 days as after two weeks, twins can no longer form, and so it is deemed that an individual has started to develop.

The time limit has remained unchallenged while scientists were unable to keep embryos alive beyond seven days, but the new breakthrough could lead to calls for the threshold to be extended.

Professor Zernicka-Goetz said it would be useful to be allowed to follow the development of embryos for a ‘a few more days’ after the current cut off period.

The Nuffield Council on Bioethics is also planning a meeting on the possibility of changing the limit.

Prof Robin Lovell-Badge, Group Leader, The Francis Crick Institute, said: “Proposing to extend the 14-day limit might be opening a can of worms, but would it lead to Pandora’s box, or a treasure chest of valuable information ?

“This is not a question to be left to scientists alone.”

The embryos used in the research were donated by couples undergoing fertility treatment.

The research was published in the journal Nature.