Mobile phones do not pose health problems to adults in the short term but there is a "slight hint" of a cancer risk for long-term users, according to the results of a study which could not rule out risks of brain or ear cancer for those who have used mobiles for more than 10 years.

"We found no association between incidence and exposure for people who have used their phones for less than 10 years," said Lawrie Challis, chair of the Mobile Telecommunications and Health Research programme. "But we cannot rule out the possibility [of] an association for exposures for more than 10 years. The numbers appeared to show some slight hint ... it's a faint suggestion that needs to be followed up."

The researchers involved in the six-year study said they would further investigate in the next phase of their work, which would also examine the effects of mobile phones on children's health.

The £8.8m MTHR programme is a joint project funded by government and the mobile phone industry in response to Sir William Stewart's independent inquiry in 2000 into the safety of mobiles. He has concluded that mobile phones seem to pose no problems but has recommended further research.

The group's report, published yesterday, collates the work of 28 studies it has backed, as well as other research from around the world that has looked at the effects of mobile phones on health factors such as blood pressure, brain function and cancer. It concludes that there is no evidence of short-term effects from either GSM or 3G handsets or base stations.

There is also no evidence, the researchers say, of the phones causing the symptoms described as electrical hypersensitivity, a phenomenon affecting up to 4% of people in the UK who describe a sense of tingling or dizziness in the presence of electrical signals.

For the long term, however, there is less certainty. Paul Elliott, an epidemiologist at Imperial College London, said: "In some of the studies there was an excess of malignant brain tumours and acoustic neuromas [ear cancers]. But the excess is quite small and is at the borderline of statistical significance."

Regarding the question over the effects of mobiles on children, Professor Challis said: "At this stage we have no evidence at all that mobile phones or masts hurt children. But we do know that [regarding] a number of other environmental agents - lead, tobacco smoke, ultraviolet radiation, ionising radiation - children react differently to them and often more severely, than do adults."

The professor said that his group's findings did not contradict the advice from Sir William, who, in 2005, urged parents to limit their children's use of mobile phones as a precaution, and advised that under-eights should not use them at all.

Starting next year the MTHR researchers will begin a £6m health study on more than 200,000 mobile phone users from across Europe.