Since the NHS breast screening programme was introduced in 1988, research has been continuing into ways to make it more effective.

Doctors have found that taking two X-rays during screening, rather than the usual one mammogram, improves the breast cancer detection rate by 24 per cent.

Trials are going on to determine whether screening should be offered to women under 50, and to establish the most appropriate time interval between screening visits. Pilot projects into increasing the screening age are also under way.

Mammography is the only breast screening method whose value has been shown in random trials. The policy in Britain is to offer women aged 50- 64 a mammography every three years.

Women under 50 are not offered screening as mammography has not been seen to be beneficial for this age group. Although studies are going on, so far there is little data on the screening of younger women.

It appears that mammography detects different sorts of lesions in younger and older women and is not so effective at detecting clinically important cancers in younger women. Women under 50 seem more likely to get false negative or false positive results from mammography. This means they are more likely to be recalled for tumours which turn out to be benign - and more likely to have malignant tumours missed. Small, malignant tumours seem more difficult to spot in younger women, partly because of breast density and partly because tumours grow faster in older women.

Dr Trevor Powles of the Breast Cancer Unit at the Royal Mardsen admits that previous trials would not appear to support screening for younger women. "Having said that," he adds, "a day doesn't go by when I don't see a young woman who's got clinical breast cancer we can see on X-ray. Perhaps we need to look at new techniques for mammograms, more sophisticated ultrasound, the use of MRI, to see if we can develop a useful screening programme for the under 50s."

The government's aim is to reduce breast cancer deaths by a quarter in the population of women to be screened. Figures published for the 1994/5 screening programme show that 6,500 women aged 50 or over were found to have cancer.

This raised the total number of women who were able to receive early and potentially life-saving treatment for breast cancer since the programme began to more than 32,500.

Of course, if the figures are to be achieved, women have to continue to be persuaded it is their best interests to come forward for screening. Almost 77 women in every 100 now take up the invitation and almost 90 per cent of women who have been screened before come back three years later.

National co-ordinator Julietta Patnick says: "This is a heartening endorsement of our programme and shows how hard we have worked to offer a friendly service while maintaining high technical quality."

Women over the age of 65 are not routinely invited for breast screening, although they can make their own appointments. Not everyone is happy with this. The NHS Breast Screening Programme has teamed up with Age Concern to inform this age group of their right to request breast screening every three years, but warn the service could not cope with the increase in numbers if they were automatically included.

Some cancer specialists - including Dr Powles - would like to see screening extended to include all women up to the age of 70. He says: "A woman of 66 has a 20-year life expectancy. She stands to gain 20 years if screening works. Screening is more effective in a women over 66 than one of 50 because her breasts are less dense."