We found the levels of radiation were well within guidelines and not hazardous

Simon Mann, NRPB

But experts, writing a report for the National Radiological Protection Board (NRPB), the government's official watchdog, said the levels given off were so low that they were incapable of causing bad health.

On average, the exposure was just 0.002% of the maximum recommended by international guidelines.

And the experts found that roofs actually absorbed even more of this radiation.

In some tests, pupils were receiving a higher dose of radiation coming through the window from a mast 300 yards away than through the roof from the mast sited on top of the school.

Mobile phone use has soared

There are approximately 25m mobile phone in use in the UK, but this figure is expected to increase, and the demand for new locations for masts is ongoing.

Despite the finding, NRPB deputy director John Stather said more extensive research was needed.

He supported the recommendation in the recently-published Stewart report on mobile phone safety which suggested the creation of a database of mobile phone masts which could then be cross-referenced against health problems.

Simon Mann, one of the authors of the NRPB study, said: "There was a real need for someone to produce some independent data that could be held up for everyone to see.

"We chose places to investigate where people were concerned about masts but in all of them we found the levels of radiation were well within guidelines and not hazardous."

The early results of the study had been passed to the Stewart inquiry.

Its conclusions suggested that although mobile phone masts themselves were unlikely to cause health problems, the worry and stress associated with living near the mast might well trigger illness.

It also recommended a "precautionary approach" for mobile phone users, particularly children, saying there was no evidence that this caused health problems, but no proof that it did not.

In all, the NRPB team tested 118 points at 17 different mast sites.