Scientists at the Cancer Research Campaign say men exposed to radiation may suffer damage to their sperm, which in turn increases the risk that their offspring will contract the blood cancer.

But their work so far concludes that exposure alone is not enough to trigger leukaemia and other, as yet unknown, factors must be involved.

Greater susceptibility

Scientists from the Paterson Institute for Cancer Research in Manchester isolated the effect in mice.

The Head of the Research Team, Dr Brian Lord, said: "There is no doubt that the group of animals that were the product of preconceptional paternal irradiation (PPI) had a greater susceptibility to the induction of leukaemia."

However Dr Lord, an expert on the effects of plutonium on the development of the blood system, emphasised more research was required.

The findings did not explain the outbreak of clusters of the disease in children living near nuclear power plants.

"But what it does show us, for the first time, is a potential way in which paternal irradiation can lead to an increase in leukaemia risk for the next generation. It shows us how DNA defects can be passed from generation to generation," he added.

Risk doubled

The research, published in the British Journal of Cancer, showed that the radiation produced genetic changes in the makeup of the cells and some of the damage was passed on to the next generation of mice. The risk of developing leukaemia was nearly doubled in the PPI mice.

The damage in the bone marrow cells alone was not enough to cause the leukaemia, but it increased vulnerability to the disease. Leukaemia developed earlier and more frequently in the cells when they were exposed to a powerful cancer-causing chemical.

Cause unknown

Scientists are not sure what causes cancer. Genes certainly play a part and certain chemicals, substances called carcinogens, are also involved.

Prof. McVie: Radiation an important factor

The Director General of Britain's Cancer Research Campaign charity, Professor Gordon McVie, said some scientists believed that cancer required two factors to combine to develop. Radiation could be one of those factors.

Second factors could include a virus or a genetic defect inherited from the mother.

Scientists have been debating whether radiation causes childhood leukaemia for many years. A controversial study in 1990 claimed that a cluster of cases in northern England resulted from parents working at the Sellafield nuclear power plant in Cumbria.

Other studies of atomic bomb survivors and people who have had radiotherapy found no evidence to support the theory.