If these can be used to grow healthy tissue which can safely be transplanted into elderly patients it could open up new avenues of treatment for the elderly, say the scientists.

"This is a new paradigm for cell rejuvenation... the age of cells is definitely not a barrier to reprogramming," `The Daily Telegraph` quoted Jean-Marc Lematre, who led the study, as saying.

Embryonic stem cells can grow into any type of tissue in the body, and scientists hope they could one day be used to replace diseased organs with healthy, lab-grown replacements.

But their use in medicine is controversial as it involves the destruction of human embryos, albeit at a very early stage.

As an alternative, a method of taking normal cells from adults and reversing them to an unspecialised state, known as induced pluripotent stem cells (iPS) can be used, making them almost indistinguishable from embryonic stem cells.

But many experts are divided over whether the technique can work efficiently in elderly patients, who have the most to gain from the potential treatments, because their cells have deteriorated further.

By adding two new ingredients, known as transcription factors, to the method of generating adult stem cells, the team was able to overcome this hurdle and "reset" many of the key markers of ageing in cells.

There is a long way to go before the "proof of concept" could be translated into treatments, the team said.

Experts have welcomed the findings published in the `Genes & Development` journal.

Mick Bhatia, director of the Stem Cell and Cancer Research Institute at McMaster University in Canada, said: "I think it is certainly interesting that they are saying some of these age markers reversed and the age programming has made the cells youthful."