Debate over the safety of wireless networks has been reignited after Panorama claimed last night that a school using Wi-Fi recorded radiation that was three times as high as that coming from a mobile phone mast.

Sir William Stewart, chairman of the Health Protection Agency, claimed in the programme that there was evidence that low-level radiation coming from devices such as mobile phones and Wi-Fi could damage health. 

He said there should be a review of Wi-Fi, which is now used in many homes, schools and in some areas being rolled out in towns and cities.

The claims are similar to those that have dogged mobile phones, although to-date there has been no conclusive evidence that they are a health risk.

Some scientists poured scorn on Stewart's comments, pointing out that Wi-Fi uses radio waves, which have been around for over a century without damaging people's health.

Ben Goldacre, a medical doctor who runs the Bad Science website, stated that the programme makers had made melodramatic, misleading television instead of an informed documentary. 

"In 28 minutes of TV you could have given a good summary of the research evidence so that people could make their own minds up. But that would not get you as many viewers," he said.

Goldacre explained that there had been over 30 double-blinded studies looking at people who believe they have symptoms caused by 'electromagnetic hypersensitivity'.

In these studies, subjects were told that they were being exposed to electromagnetic signals without knowing when the signal was switched on and told to say when they felt the effects.

These studies have consistently shown that there is no relationship between symptoms and the presence of an electromagnetic signal.

There was also no specific reason to believe that Wi-Fi was different or more dangerous than other familiar signals, such as those from radio or TV. "Wi-Fi is also just next door to CB radio and police radio," said Goldacre.

If problems such as cancer can occur, the incidence will be rare because prolonged exposure to radio and TV signals has yet to produce cancer clusters, he added.

Professor Olle Johansson, of the Karolinska Institute in Sweden, told Panorama: "If you look in the literature, you have a large number of various effects like chromosome damage, you have impact on the concentration capacity and decrease in short-term memory, and increases in the number of cancer incidences."

Johansson has long been warning of the damaging effects that electromagnetic signals can have on people.

Professor Lawrie Challis, chairman of the Mobile Telecommunications and Health Research programme management committee, told the BBC that it was unlikely that Wi-Fi would "pose any risk to health".

"Wi-Fi exposures are usually very small," he said. "The transmitters are low power and some distance from the body."

But Professor Challis did suggest that people use laptop computers on a table rather than their lap.

Some schools are now coming under pressure from parents and teachers to stop using wireless networks until it is known whether or not the low-level radiation can damage children's health.