Long-term use of mobile phones may cause cancer, government scientists have admitted, as the biggest review ever of the subject is published.

The report, by a Health Protection Agency group set up to examine the safety of mobile phones, transmitter masts and Wi-Fi, found "no convincing evidence" that they caused any adverse effects on human health, The Telegraph reported.

But members of the Advisory Group on Non-ionizing Radiation (AGNIR) said they could not be sure of the long term effects of mobiles, as there was currently "little information beyond 15 years from first exposure".

A small number of individual studies have found evidence of a link between heavy mobile phone use and increased brain tumor incidence.

Two years ago the INTERPHONE study reported that the heaviest users could be at a 40 per cent increased risk of developing glioma, a common type of brain cancer. Most studies have found no such association though.

However, brain tumors can take decades to develop. Launching the 333 page report, which reviews hundreds of studies, group chairman Professor Anthony Swerdlow said: "I think there's a need to keep a watch on national cancer trends in relation to this, particularly with brain tumors.

"So far brain tumor rates are not rising in the sorts of age groups who have had exposure for 10, 15 years.

"But if this is something that takes 15, 20 years or more to show up, we need to keep watch over rates just in case."

Researchers running cohort studies - projects following individuals' health over their lifetimes - also needed to investigate the matter to see if heavy users of mobile phones tended to develop brain tumors more than others, said Prof Swerdlow, an epidemiologist at the Institute of Cancer Research.

The review found no evidence that radio frequency (RF) electromagnetic fields caused by Wi-Fi - now widespread in schools, homes and the workplace - caused harmful effects, or could even be detected by those who claimed to be sensitive to it.

Neither did it find any evidence that mobile phone mast transmitters caused health problems.

The HPA is though continuing to adopt what it calls a "precautionary approach" to mobile phone use, in particular advising that children avoid their "excessive use".

Dr John Cooper, director of the HPA's Centre for Radiation, Chemical and Environmental Hazards, commented: "There is still no convincing scientific evidence that radio frequency (RF) fields exposures from mobile phones and other radio technologies affect human health at exposure levels below internationally agreed guidelines.

"However, as this is a relatively new technology, the HPA will continue to advise a precautionary approach and keep the science under close review.

"The HPA recommends that excessive use of mobile phones by children should be discouraged and mobile phone Specific Energy Absorption Rates (SAR) values should be clearly marked in the phone sales literature."

Dr Simon Mann, another member of AGNIR, said: "We are continuing to recommend discouraging non-essential use by children."

Texting was preferable to calling, he said, as it meant the phone was "tens of centimeters away (from the head) rather than one or two", reducing exposure levels by "orders of magnitude".

He added: "Hands-free kits reduce your exposure, as does using third generation (3G) modes rather than second generation (2G), and shorter calls."

Last spring the Department of Health updated its advice by saying that sending text messages or using hands-free kits can reduce exposure to radiation, by keeping the handset away from the head.

John Cooke, executive director of the Mobile Operators Association, said: "The public will be reassured by this conclusion that there is still no convincing evidence that mobile phones cause adverse health effects, after almost two decades of research involving a large number of studies."