Fat from the tummy or bottom could be used to grow new breasts in a treatment which could be carried out in an hour - or a lunch break.

Scientists say they can create a fat mixture with concentrated stem cells, which, when injected into the breast, apparently encourages tissue to grow.

The therapy, detailed in Chemistry and Industry Magazine, could help cancer patients who have had mastectomies.

And if licensed, it may rival silicone for those seeking bigger breasts.

Using fat from the patient's own body to rebuild other areas is not a novel idea, but such reconstructions often fail as the fat is simply reabsorbed.

However using fat-derived stem cells appears to overcome this problem, according to the company behind the procedure, Cytori Therapeutics.

Scientists say they are not sure quite how it works, but suspect that the stem cells emit signals that encourage blood vessels to grow and nurture new tissue.

Rajiv Grover of the British Association of Aesthetic Plastic Surgeons (Baaps) said he saw the research as a "positive development for medical science", but doubted whether it would provide any immediate results in cosmetic surgery.

"We need to find out how these cells work once they are in the breast before any great claims can be made."

Antonia Dean, a clinical nurse specialist at Breast Cancer Care also said more work needed to be done - "both in terms of how long the new breast really lasts for, but most importantly the safety implications for women who have had tumours."

Filling out

The procedure - dubbed Celution - could be carried out in an hour.

Fat from the either the stomach, bottom or thigh can be taken out with a standard liposuction procedure, and the stem cells then extracted.

These cells are placed into a cartridge ready for injection one hour later. The company says the breasts will then fill out over the course of six months.

The largest trial so far has involved 19 women in Japan. All of them had had at least partial mastectomies and all responded well to the treatment, with no major side-effects.

Clinical trials are continuing, and the company hopes to introduce the therapy to Europe in early 2008.

It is expensive - costing a few thousand pounds per cartridge, but this is not dissimilar to the price of conventional surgery.

In the UK, about 45,000 people are diagnosed with breast cancer each year. Of these about 30% will have mastectomies.