Breast cancer screening in the UK may be causing more harm than good, according to new research.

Experts found women may be likely to be harmed by the programme and undergo unnecessary surgery, especially in the first decade of being screened.

James Raftery, professor of health technology assessment at the University of Southampton, led the new study which examined data from the 1986 Forrest report.

The Forrest report, which led to the introduction of breast cancer screening in the UK, determined the benefits of screening in terms of quality adjusted life years or QALYs (a measure of quantity and quality of life).

It found about 3,000 QALYs in terms of lives saved over a 20-year period for every 100,000 women who were invited for screening. But at the 10-year mark, the number of QALYs stood at only about 1,000.

In the new analysis, published in the British Medical Journal (BMJ), Prof Raftery and his colleague Maria Chorozoglou included estimates of the risk of women being harmed, which were not included in the Forrest report.

Harms include false positives (abnormal results that turn out to be normal) and over-treatment (treatment or surgery on harmless cancers that would never have caused symptoms or death during a patient's lifetime).

The new research found that once harms were included, the QALY benefit in terms of lives saved was only 1,500 QALYs after 20 years - half the figures quoted in Forrest. And, in the first few years of screening, women were, on average, more likely to be harmed than to see any benefit.

Prof Raftery said: "At up to eight years, the harms generally outweigh the benefits but at 20 years there are greater positive benefits. Nevertheless, either way, the benefit to patients is less than was stated in Forrest."

He said the vast majority of women undergoing surgery to remove a suspected cancer did not actually need the treatment.