Using a mobile telephone more than doubles the risk of developing brain cancer on the side of the head where the phone is held, the British Association festival of science was told September 4.
A second warning was issued when Sir William Stewart, who chaired last year's government-sponsored report into mobile phone health risks, called for the cost of handsets to be increased to restrict their use by children.
Sir William, the president of the British Association, said he would not allow his grandchildren to use a mobile phone and also castigated operators for targeting advertisements at youngsters.
The study into a link with brain tumors was carried out by Lennart Hardell, professor of oncology at Orebro University in Sweden, who compared 1,617 patients diagnosed with brain tumors between 1997 and last year with the same number of healthy people.
He found that people who used cell phones were two and a half times more likely to have a temporal brain tumor on the side of the head where they held their phone.
In the case of tumors of the auditory nerve, which connects the ear to the brain, the risk increased to more than three times for mobile phone users.
Because of the need to investigate patients who had used cell phones for 10 years or more, the research concentrated on analogue phones. But Prof Hardell said yesterday that users of digital mobiles, which emit less radiation, could face similar health risks because the phones use pulsed microwaves as opposed to the continuous signals of analogues.
Prof Hardell said: "We will have to wait several more years, probably at least until 2005, before we can see the health effects of digital phones." Meanwhile users should exercise precaution, as the Stewart report has urged.
The mobile phone industry has been plagued by reports suggesting that mobile phones cause cancer. However, there have also been reports of studies showing no health risks to users.
With more than 800 million cell phones in use worldwide, of which 44.7 million are in Britain, even a small cancer risk could have devastating effects.
Sir William said the investigation into the potential dangers of using a mobile phone needed to be broader. "Research into mobile phones has been led by the physical sciences looking at radiation levels. But there are subtle biological effects.
"They could be adverse or beneficial - we simply do not know. There is increasing evidence that the non-thermal effects of mobile phone radiation could affect us. We should be doing more work on biological effects and the Department of Health agrees with that."
Sir William added that it was "irresponsible" for operators to suggest in advertisements that youngsters needed a mobile phone to return to school.
Explaining why he would not allow his grandchildren to use mobiles, he said: "Children's skulls are not fully developed. Their bones are not as thick as adults and they will be using mobile phones for longer over their lifetimes than adults.
"It is worrying as there are effects we will not know about for some time. I would support higher pricing to reduce use of mobiles by children."
A report by the National Radiological Protection Board has called for more research into the police radio system, Tetra, because of suspicions that its similar technology to digital phones - using pulses of around 17 cycles a second - could affect brain tissue
www.News.telegraph.co.uk September 5, 2001