The "parent cells" have the ability to develop into many other cell types in the body, and scientists believe they have huge potential to treat diseases or injuries that do not currently have a cure.

But they are also inherently unstable and begin to mutate into other cells as soon as they are created making it difficult to store them for more than a day or two.

Now scientists at the Universities of Bath and Leeds have discovered a chemical that can be added to embryonic stem cells grown in the laboratory, allowing them to multiply without changing into other cell types.

Professor Melanie Welham's team at the University of Bath's Department of Pharmacy & Pharmacology, collaborating with Professor Adam Nelson at the University of Leeds said breakthrough will help scientists produce large stocks of cells that are needed for developing new medical therapies.

Professor Welham, who is co-director of the University of Bath's Centre for Regenerative Medicine, added: "Stem cells have great potential for treating spinal injuries and diseases like type I diabetes because they can change into a range of specialised cell types including nerve or pancreatic cells, which could be used to repair damaged tissues.

"Unfortunately, when you grow stem cells in the lab, they can spontaneously develop into specialised cells, making it difficult to grow large enough stocks to use for medical research.

"We've identified a chemical that will put this process on hold for several weeks so that we can grow large numbers of them in their unspecialised state.

"This is reversible, so when you take it away from the cells, they still have the ability to change into specialised cells."

Professor Adam Nelson's team, at the Astbury Centre for Structural Molecular Biology, made more than 50 chemical compounds that were tested for activity in the stem cells.

"The researchers found that the chemicals worked by blocking an enzyme, called GSK3, that can control when the stem cell switches to a more specialised cell type

by:telegraph