Doctors at Southend Hospital, Essex studied 2,000 lung cancer patients.

A third of women, compared to a quarter of men, had small cell carcinoma.

Researchers also found an increased incidence of lung cancer in women who had never smoked.

Eight per cent of women had never touched cigarettes compared to 1.9% of men - although only 4% of all the lung cancer patients studied were "never-smokers".

We must work together far harder to prevent young women today becoming the lung cancer victims of the future

Dr John Harvey, British Thoracic Society

They were more likely to have a different type of lung cancer called adenocarcinoma.

The research was presented to the winter meeting of the British Thoracic Society.

Doctors are not certain how to explain either finding.

But they suggest genetic and hormonal influences, biochemical differences, women's smoking habits, air pollution and passive smoking could play a role.

Separate research by University of Cambridge scientists found that women are genetically more susceptible to emphysema than men, especially if they smoke.

Quitting

Experts remain concerned at the number of young smokers.

There was a higher proportion of "current smokers" in the younger age range of both men and women.

Women's smoking habits give most concern, however.

The Southend study showed fewer women than men had managed to stop smoking.

Only 51% of women in the study had quit compared to 60% of men.

And increasing numbers of teenage girls took up smoking in the 1990s, who experts warn could become the lung cancer cases of the future.

The researchers suggest women's smoking habits are 20 years behind men's.

Smoking peaked in women in 1966 when 46% smoked. The number of men smoking in the population peaked around 20 years before at a higher level and has declined more rapidly.

Anti-smoking campaigns

Dr Dennis Eraut, a consultant physician at Southend Hospital who led the study, told BBC News Online the study had not looked at why women were affected by lung cancer differently.

"It could be because of genetic, hormonal or biochemical differences between men and women.

"Some women have families where there is quite a lot of cancer occurring."

He added: "Non-smokers might have been exposed to their husband's smoking."

"Our research shows that women are still at great risk of developing lung cancer - a trend that looks likely to continue.

Dr Eraut added: "Quitting smoking is so important for both men or women to help prevent lung cancer occurring in the first place - and that health professionals must work together to help smokers kick their habit."

Prevention

Dr John Harvey, chairman of the BTS communications committee, said: "We applaud the government's �15m investment in harder-hitting anti-smoking campaigns but we would urge ministers to take note of this study.

"We must work together far harder to prevent young women today becoming the lung cancer victims of the future."

Dame Helena Shovelton, chief executive of the British Lung Foundation, said: "We have been aware for some time that the number of women smoking, especially those under 30, is on the increase.

"Unfortunately this in turn will lead to an increase in the number of women with lung cancer."

"In addition more and more women are exposed to passive smoking which we know can cause lung cancer.

"And as our recent report showed, smoking cannabis also has lung cancer risks."