A traditional herbal tea may hold the key to fighting breast cancer, claim scientists.

Extracts from the plant known as virgin's mantle, which is used as a medicinal tea in some countries, can kill cancerous cells in the test tube.

The plant-based tea is already drunk by women in rural Pakistan who have breast cancer, but until now its use as a treatment has been regarded as folklore.

Research by scientists at Aston University, Birmingham, and Russells Hall Hospital, Dudley, suggests it contains potent anti-cancer agents that act singly or in combination against the proliferation of cancer cells.

Laboratory tests showed they arrested the growth of cells within five hours of application and caused them to die within 24 hours.

The plant, which has the botanical name Fagonia cretica, is found in arid, desert regions of Pakistan, India, Africa and parts of Europe.

Professor Helen Griffiths and Professor Amtul R Carmichael, who headed the study, found herbal tea made from the extract of the plant destroys cancer cells but, unlike conventional chemotherapy, treatment does not damage normal breast cells, thus reducing side effects.

Reports from breast cancer sufferers in Pakistan suggest the plant extract does not trigger any serious side effects such as loss of hair, drop in blood count or diarrhoea.

The research, published in the science journal PloS One, found the plant extract had a novel mechanism which could remedy defects in cell DNA that would normally resist tumour growth.

An impaired DNA response not only allows the cancer to flourish, it also inhibits the way chemotherapy works which reduces its effectiveness.

Professor Carmichael said a small hospital 100 miles north of Lahore in Pakistan started using the herbal tea 40 years ago to treat breast cancer patients.

She said: 'It appears to keep them in remission, although we can't use the word cure at this stage.

'However, they live for a long time without losing their hair or putting on a large amount of weight, or experiencing other toxic side effects associated with chemotherapy, so we are confident this extract has something to contribute.'

She said stringent safety tests would be needed in developing a drug based on the extract.

At present the herbal tea is being used to treat Asians but there might be different effects in Caucasian patients, she added.

Professor Griffiths said more research is needed to establish the role of the extract in cancer management, and it now needs to be demonstrated that this extract is as effective in killing cancer cells inside the body as it is within a laboratory.

She said the next steps are to identify which element of the plant is responsible for killing the cancer cells with a view to eventually running trials with cancer patients.

Dr Caitlin Palframan, policy manager at Breakthrough Breast Cancer, said: 'Some of the most important cancer-fighting drugs are originally derived from plants.

'As this research is at the very earliest stage, we won't know for quite some time whether drugs derived from this plant will be effective in treating breast cancer but we look forward to seeing any progress.

'We would advise women with breast cancer who are considering using any herbal remedies to discuss this with their doctor first as some may interfere with ongoing cancer treatment.'

Emma Pennery, clinical director of Breast Cancer Care, said: 'Much more research would be needed to build on this small-scale laboratory work to date.'