Fears that mobile phone masts on top of schools are bombarding pupils with high levels of radiation have been dismissed by a national radiation watchdog.

Tests by the Harwell-based National Radiological Protection Board found roofs soaked up the radiation emitted by masts, so levels absorbed by children inside classrooms were very low.

In fact, in some cases, pupils were found to be absorbing more radiation from masts over 300 yards away from the one on the roof of their classroom.

The NRPB carried out tests on 118 different points at 17 sites, at masts, known as base stations, near schools, and outside offices and homes.

Last October, Oxfordshire County Council ruled masts should not be located within 200m of a school, although masts were already installed near five schools, earning them an estimated 21,000.

Although headteachers should be able to get rid of the masts once the lease is up, a loophole means the phone operators could insist the structures stay where they are.