A £20million, decade-long investigation overseen by the World Health Organisation (WHO) will publish evidence that heavy users face a higher risk of developing brain tumours later in life,
The conclusion, while not definitive, will undermine assurances from the government that the devices are safe and is expected to put ministers under pressure to issue stronger guidance.
A preliminary breakdown of the results found a “significantly increased risk” of some brain tumours “related to use of mobile phones for a period of 10 years or more” in some studies.
The head of the Interphone investigation said that the report would include a “public health message”.
Britain’s Department of Health has not updated its guidance for more than four years. It says that “the current balance of evidence does not show health problems caused by using mobile phones”, and suggests only that children be “discouraged” from making “non-essential” calls while adults should “keep calls short”.
In contrast, several other countries, notably France, have begun strengthening warnings and American politicians are urgently investigating the risks.
The Interphone inquiry has been investigating whether exposure to mobile phones is linked to three types of brain tumour and a tumour of the salivary gland.
Its head, Dr Elisabeth Cardis, backed new warnings.
“In the absence of definitive results and in the light of a number of studies which, though limited, suggest a possible effect of radiofrequency radiation, precautions are important,” she said.
“I am therefore globally in agreement with the idea of restricting the use by children, though I would not go as far as banning mobile phones as they can be a very important tool, not only in emergencies, but also maintaining contact between children and their parents and thus playing a reassurance role.
“Means to reduce our exposure (use of hands-free kits and moderating our use of phones) are also interesting.”
The project conducted studies in 13 countries, interviewing tumour sufferers and people in good health to see whether their mobile phone use differed. It questioned about 12,800 people between 2000 and 2004.
Previous research into the health effects of mobile phones, in the short time they have been in use, has proved inconclusive. However, a breakdown of the latest findings, seen by The Daily Telegraph, shows that six of eight Interphone studies found some rise in the risk of glioma (the most common brain tumour), with one finding a 39 per cent increase.
Two of seven studies into acoustic neurinoma (a benign tumour of a nerve between the ear and brain) reported a higher risk after using mobiles for 10 years. A Swedish report said it was 3.9 times higher.
A summary said a definitive link could not be proved because of difficulties with subjects’ memories.
An Israeli study found heavy users were about 50 per cent more likely to suffer tumours of the parotid salivary gland.
The Interphone inquiry has faced criticism for including people who made just one call a week, and leaving out children, which some experts said could underplay the risks. Some results for short-term use appeared to show protection against cancer, suggesting flaws in the study.
The final paper, funded partly by the industry, has been delayed as its authors argued over how to present the conclusions. But it has been sent to a scientific journal and will be published before the end of the year.
A spokesman for the Health Protection Agency said there was “no hard evidence at present” of harm to health. Use by children for non-essential calls should be discouraged, he added.
A spokesman for the Mobile Operators Association said more than 30 scientific reviews had found no adverse health effects.
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