The national programme currently routinely screens women aged 20-64.

But research by a team Wolfson Institute of Preventative Medicine at St Bartholomew's Hospital, London, has found that it would be more effective to screen women until the age of 69 than to continue to screen women aged 20-29.

The researchers based their conclusions on calculating how many life years are saved by screening women at different ages, assuming that if women did not develop cervical cancer they would live to the age of 80.

"Focusing on young women as was done a few years ago was illogical and ill-judged," the researchers report in the Journal of Medical Screening.

"Extending the offer of cervical smear examination to women aged 65-69 would be reasonable, preventing deaths up to the age of 80 and beyond."

Dr Malcolm Law, one of the Wolfson team, said: "In a nutshell we're saying that the age distribution for screening needs to be shifted up a bit.

"Target the age group where you can do most good.

"We are not suggesting that we only screen that peak period. We are saying that is the optimum."

However, the Cancer Research Campaign, which funded the research, has stressed that its findings should not be used as an argument for scrapping cervical cancer screening for women aged 20-29.

Kate Law, head of clinical programmes, said the research failed to consider the fact that cervical cancer screening picked up many cases of young women who were at a pre-malignant stage of the disease.

Approximately 2,000 women a year develop pre-malignant carcinomas by the age of 20. Another 4,000 develop the symptoms by the age of 25.

Ms Law said it was vital that screening continued to identify these women so that they could be treated before they developed cancer.

"We are totally in favour of screening of the elderly," she said.

"It was thought that as these women had never been screened in their lives they might be reluctant to attend, but there is evidence to suggest that if they are recommended to do so by their GP, they will go, and they will benefit from it without question."

Julietta Patnick, national co-ordinator of the NHS breast and cervical screening programmes, doubted that there was any value in extending the screening programme to older women.

Screening is a success

Breast cancer screening should also be extended

She said the current programme, which was launched ten years ago, had already succeeded in reducing the peak age at which women developed the disease.

Women born in the 1950s were most likely to develop cervical cancer in their thirties.

This contrasted with women born in the 1920s who had not benefited from screening, and who were most likely to develop the disease in their seventies.

The Wolfson team also found that it would be desirable to extend the breast cancer screening programme to women aged up to 74.

At present, the mammography programme targets women aged 50 to 64.

Mrs Patnick said a pilot scheme was already under way to test the merits of screening woman aged 64 to 69.