The BBC's John Kay explains the significance of the research

Researchers in the UK say they have found significant evidence that could explain the long-suspected links between the cables and childhood cancer.

A team at Bristol University, led by Professor Denis Henshaw, unveiled its findings at a conference of international specialists in Bristol on Thursday

However, the claims were described as "alarmist speculation" by Dr John Swanson, a spokesman for the Electricity Association, the industry's trade group.

Dr John Swanson on BBC Radio 4: "Implausible and purely speculative"

"It is still the case that the weight of scientific evidence is against there being a link between electromagnetic fields and ill health," he said.

Many of the ideas in Professor Henshaw's research had been previously dismissed by the government's National Radiological Protection Board as "implausible and purely speculative".

"However, he has put forward some new ideas and it is for the science community to test these," Dr Swanson said.

"What we should not be doing is alarming people. It is wrong to cause anxiety and alarm.

"As a father with two young children I would have no qualms about living near a power line."

Dr David Jeffers, a spokesman for the National Grid, also doubted the Bristol research.

He said that other independent university researchers had tried and failed to replicate the team's results.

Increased exposure

Electricity producers say there is no proven risk

The researchers disclosed the findings at a conference on the health effects of electromagnetic (EM) field exposure.

Professor Henshaw said there were "mechanisms" which increased exposure to environmental pollutants near high-power sources.

"We believe that pollutants in the air, notably from car pollution, are actually agitated by the effects of the power lines," he said.

He said that this happens "in a way which leads to an increased exposure to individuals under power lines".

Leukaemia levels

Professor Henshaw denied there was a lack of evidence to back up his theories.

Professor Denis Henshaw talks to the BBC's Clinton Rogers

He said: "We already know the increased level of childhood leukaemia under power lines - it is about a factor of about 1.5."

Professor Henshaw's team recently published results of experiments near a National Grid line in a farm field in South Gloucestershire, near Bristol.

The study concerned the attractive effect of the power cable on aerosols, airborne droplets carrying cancer-causing agents, viruses or bacteria.

Proximity affects risk

It showed an increased risk of exposure, the nearer a person moved towards the cable. The team said further research was needed to see if there was also an increased dosage risk.

The experiments were carried out in both summer and winter, but the results did not vary greatly despite the differing weather conditions.

The team suggested that the attractive effect on the aerosols may be the missing link between the cables and childhood cancers, such as leukaemia.