Family organisations have criticised an Oxford-based cancer charity for 'scaremongering' with research claiming older parents are more likely to have children with leukaemia.

Cancer Research UK has revealed results of a study by the city's Childhood Cancer Research Group, which claims mothers aged 30 to 35 are 30 per cent more likely to have a child who will develop the blood cancer.

In a press release published yesterday headed Cancer risk for children of having older parents, the charity warned the risk increased by 88 per cent for mothers over 40.

Researchers, led by honorary senior research fellow Dr Gerald Draper, said a similar pattern was also true for fathers.

Parent groups criticised the report and claimed mothers and fathers were becoming tired of information about the threats to pregnancy in older people.

Dr Draper admitted that the actual chances were very small and that people should not be alarmed.

National Family and Parenting Institute press officer Christian Jenner said it was important the research was not taken out of context.

She said: "This seems to be an incredibly low risk -- you're more likely to be hit by a bus.

"Researchers can't stop reporting their findings, but how the media will respond about this is important.

"What headlines will be screaming at parents to alarm them? Planning a family is an anxious time for parents anyway and does this really help?"

Helen Humphrey, editor of the UK Parents website, which has 12,000 registered users, and a dedicated forum for older parents, said: "I'd say that when women reach a certain age it's commonly known there's a risk in pregnancy and I don't think it puts them off having children.

"But they're constantly bombarded with information -- this research and that research -- and they're getting a little tired of being scared of all the things that could go wrong. Apparently, you get to a certain age and you should start to hurry up trying for a family -- but why? There really is not that much of a risk."

Dr Draper's research covered 18 years and studied more than 3,000 cases of acute lymphoblastic leukaemia which is the most common form of the disease and is diagnosed in 325 British children under 15 every year.

He admitted the risks were lower than those of Down's Syndrome, which can affect children born to older mothers.

A woman in her 20s has a one-in-2,000 chance of giving birth to a Down's baby, but the risk increases to one-in-30 for a woman aged 45.

For leukaemia, a 20-year-old woman has the same one-in-2,000 chance, but a 45-year-old would have a one-in-1,000 chance.

Dr Draper said: "We know some rare inherited genetic conditions can increase the risk of developing leukaemia and our research suggests the risk of inheriting such conditions is higher when parents are older.

"Presumably, genetic damage is more likely to be found in the eggs and the sperm-forming cells as they age.

"But the risk is actually very small and I don't think people should be alarmed by this."

His study also showed that first-born children were also more likely to develop leukaemia.

It is thought this is because they are less likely to be exposed to infections, usually spread between siblings, which can prime the immune system against later illnesses leading to leukaemia.