The National Radiological Protection Board (NRPB) said roofs soak up radiation from the masts so the levels of radiation is classrooms are low and pose no hazard.

The NRPB measured radiation levels at 118 locations near 17 sites where masts were near schools, homes and offices.

``We found that at these locations the levels were below internationally accepted guidelines,'' Dr Simon Mann, one of the authors of the report, told Reuters.

The measurements also showed that exposures of people to radio waves from nearby masts are frequently comparable to exposures from more distant masts, and from TV, FM radio and other transmitters.

But Mann admitted that there was a shortage of information and called for more research.

With the number of expected mobile phone users, which already number 25 million in Britain, expected to grow environmental groups and the public have expressed fears about the safety of mobile phone masts.

They have also called for better planning so masts can be located away from densely populated areas and schools.

A government-commissioned inquiry into mobile telephone safety warned in May that children should be discouraged from using mobile telephones because of their potential health risks.

Children have thinner skulls, smaller heads and their nervous systems are still developing which could make them more vulnerable to any potential adverse effects from the phones, the inquiry said in a report.