Wi-fi, the wireless networks which let you use a laptop on top of a hill, or a mobile phone in the middle of the ocean, are everywhere your home, the cafe, the vast majority of secondary schools and 70 per cent of all primaries. But is it bad for you?

Sensitive souls argue that the radio waves emitted by phone masts trigger everything from flu-like symptoms to headaches and even cancer, but a three year study published last month says it is all in the mind.

The research involved 56 volunteers who felt they were adversely affected by mobile phones, transmission masts and wireless computers. Twelve dropped out early because they felt unwell. The remaining volunteers were not told when the transmitter was running. Their responses were then compared with 114 “normal” volunteers. Only a handful of both groups correctly judged when the mast was on or off, and even that could be put down to chance.

The “sensitive” volunteers seemed to be making themselves ill through believing they were being harmed. Regardless of whether or not the signals were beamed at them, they experienced unpleasant symptoms. They also sweated more, indicating a heightened level of stress.

Professor Elaine Fox from the University of Essex, who led the study, says the power of the mind should not be underestimated. “It is clear that sensitive individuals are suffering real symptoms and often have a poor quality of life,” she says. “It is now important to determine what other factors could be causing these symptoms.”

These findings support earlier studies which found no firm evidence that mobile phone radiation is a health risk. But sufferers are adamant there is a link and many have had to change job or move house to shield themselves from what they perceive to be harmful radio waves.

Philip Parkin, general secretary of the Professional Association of Teachers, concedes that the number of electro-sensitives may be lower than previously thought, but insists this study does not address the potential impact on pupils. “I’ve seen research by highly reputable scientists which shows there might be a problem. There needs to be a full scientific investigation into the possible implications in schools.”

Children are thought to be more vulnerable due to their thinner skulls and developing nervous systems. But their symptoms, such as headaches, a lack of concentration and memory loss, are hard to attribute to wireless networks alone, argues Philip.

Powerwatch, an organisation which investigates the alleged health effects of electromagnetic radiation, warns that an increasing reliance on the networks is creating a dangerous “blanket of electrosmog” across the country. To date, 15,000 schools in the UK have wireless technology and it is being fitted as standard in all new state schools and academies. A typical comprehensive has 10 wi-fi transmitters spread around its premises.

“There’s been a huge growth over the past 20 years,” Philip says, “including wi-fi capabilities in nurseries. I’m not saying they should all be removed, but we need to be sure it’s safe.” So far, research has been inconclusive, he says, but a study last year by Ian Thornton from the University of Wales found a possible correlation between childhood autism and electromagnetic radiation.

A further report found that children living near overhead, high-voltage power cables have a nearly 70 per cent higher risk of developing leukaemia than others. But the research by Oxford University and published in the British Medical Journal in 2005, stops short of proving a causal link. In absolute terms, it found the extra incidence of leukaemia clocks in at just 0.02 per cent about five cases a year