The BBC's Christine McGourty: Breast cancer is more difficult to detect in younger women

The NHS currently offers breast screening once every three years to women aged between 50 and 64 years old.

Critics of screening say the money it uses would save more lives if invested into research into chemotherapy drugs and radiotherapy techniques.

Critics say money would be better spent on developing drug treatments

But two major trials, whose results are published in The Lancet, confirm that in general, breast screening saves lives.

But they also appear to show that screening women in their 40s is just as effective as screening them later in life.

The NHS Breast Screening Programme gave the report a cautious welcome, but said it was now waiting for more concrete proof.

A spokesman said: "The trial was not designed to look at the specific effects on particular age groups.

"We are therefore looking forward to the results of the Age Trial which involves inviting 65,000 women in their 40s."

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However, the results of this will not be available until at least next year.

The results of the two trials involved a total of 300,000 women.

One of them, conducted in Edinburgh, studied more than 54,000 women between 40 and 50 years old - half of whom were screened, and half who were not.

Lower death rate

After 14 years, death rates from breast cancer were 21% lower in the screened group than in the other.

The study concludes: "The results for younger women suggests benefit from the introduction of screening before 50 years of age."

East London GP Dr Gaby Tobias, who helped author a set of guidelines on how breast disease should be managed, said that a comprehensive study would be needed to persuade the screening programme to extend below 50.

She said: "People have been trying to see if this is true for a long time.

"It would be good news if it did save lives below 50, as there are a lot of tragic stories of very young women dying very quickly.

"Breast cancer tends to be quite aggressive in younger women."