Smokers hoping to start a family were warned by doctors yesterday that their habit could make them infertile and cause miscarriages and birth defects.

In a report, the British Medical Association (BMA) estimated 120,000 British men aged 30 to 50 had become impotent because of smoking. Up to 5,000 miscarriages every year were linked to smoking and passive smoking, and tobacco was implicated in 1,200 cases of malignant cervical cancer each year.

Women who smoked were also less likely to become pregnant and reduced their chances of successful fertility treatment.

The BMA published the report on the 50th anniversary of official Government recognition that smoking causes cancer. But health concerns linked to reproductive problems have been less well-documented.

Dr Vivienne Nathanson, head of science and ethics at the BMA, said: "The scale of damage smoking causes to reproductive and child health is shocking. Women know they should not smoke during pregnancy, but the message needs to be far stronger. Men and women who want to have children should bin cigarettes. Men who want to continue to enjoy sex should forget about lighting up, given the strong evidence that smoking is a major cause of male sexual impotence."

Women who smoke reduce their chances of becoming pregnant by up to 40 per cent per cycle. Mothers who smoke during pregnancy are three times more likely to have a low-birthweight baby. Smoking also increases the risk of miscarriage, stillbirth and malformations such as cleft lip.

Even after birth, the risks continue, with the children of smokers more prone to cot death, respiratory diseases and asthma. More than 17,000 under-fives are admitted to hospital every year because of breathing problems caused by smoke.

Researchers are unclear why smoking has such as massive effect on fertility and the health of the unborn child. But the report makes several recommendations, including calls for graphic pictorial health warnings on tobacco products about risks to unborn babies.

In 1950, a study by Professor Sir Richard Doll showed a link between smoking and cancer, but it was treated with scepticism. Then on 12 February, 1954, the then health minister Iain Macleod gave a press conference during which he chain-smoked and admitted: "It must be regarded as established that there is a relationship between smoking and cancer of the lung."