Radiation from hands-free mobile phones can be reduced to virtually zero by a simple tiny magnetic bead which costs a few pence, a government adviser says.
Ferrite beads are commonly used in computers to stop interference
Professor Lawrie Challis said clipping a ferrite bead on kits stops the radio waves travelling up the wire and into the head.
He called on the mobile phone industry to start using them "as standard".
The beads, which often measure less than 1cm in diameter, are commonly used to stop data interference in computers.
Professor Challis, who is chairman of the Mobile Telecommunications and Health Research Programme, told BBC News: "There is no evidence yet that mobile phones are harmful to health but people have not been using them long enough for us to be sure.
"Using a ferrite bead effectively reduces emissions to the head to zero but as yet manufacturers do not put them on hands-free kits."
And Professor Challis, who was also on the Stewart committee which looked into mobile phone safety in 2000, added: "I am not sure why, but I wish they would. They could use it as a marketing technique, you would think they would like to promote it."
While studies have shown hands-free kits reduce radiation, emissions still travel up the wires on the outside and are absorbed by the head.
The beads work by absorbing these "unintentional" emissions.
Dr Stuart Porter, of the department of electronics at the University of York, said he agreed with Professor Challis's comments.
Dr Porter, who has looked at the use of ferrite beads, said: "Hands-free kits effectively have two currents, an intentional one that stays within the wires and an unintentional one on the outside.
"It is the unintentional one the beads stop. They work by blocking the current, a bit like a block in a water pipe."
He said evidence suggested beads worked best when they were placed below the microphone on the hands-free kit, at about chest level.
But Michael Milligan, general secretary of the Mobile Manufacturers Forum, rejected Professor Challis's call for them to be used on hands-free kits.
"I agree they can have an impact. But the bigger issue is that mobile phones are tested to be comply with standards and have been passed safe."