The new findings confirmed claims that the magazine first published in April that using hands-free earpieces could more than triple the brain's exposure to radiation compared to a conventional mobile phone call. That original report was dismissed in August by the British government, which commissioned research that showed the kits did cut exposure levels.

The independent lab conducting the test took thousands of measurements to explore what was causing the changes in EMF emissions. It found that one critical factor was the distance between the top of the phone's aerial and the ear.

But consumer magazine said the methodology used in the government research was flawed. They found that the shape of the test rig used in the government tests made it impossible to get the hands-free kit wire into the position that gave the highest readings. According to the report:

We have found two possible explanations for this. First, the design of the SAR test rig doesn't replicate how someone would normally use a hands-free kit. Most importantly, the wire couldn't hang down straight - as it did when we took the highest readings in our other tests. Second, we found that the SAR test system looks for the point in the head where there is the highest level of radiation - and gives a final reading for only this area. But we found that kits and phones emit the highest levels of radiation in different places: kits emit most at the ear; phones emit most at the user's jaw and cheek.

The new research confirmed that hands-free kits could act as an aerial that channeled radiation to the ear.

The level of emissions depended on the distance between the tip of the phone's aerial and the earpiece, which varied according to how the phone was held. The government tests did not allow for this, Which? said.

According to the magazine's editor:

... it's clear that consumers can't rely on hands-free kits to reduce radiation emissions at the brain from mobile phones. Although these kits can reduce radiation, they can also increase it significantly, depending on where you position the phone and kit. Unfortunately, there is no way that consumers can work out the best position to reduce radiation.

Scientists agree that electromagnetic radiation from mobile phones warms brain tissue, some strains of mice have developed cancer in tests in Australia and Finland and that others become disorientated.

Which? said the kits could cut emissions by 10 to 90% in some positions.

In other positions they could increase them by a factor of up to 3.5.

One reason that the government's tests did not show this increased exposure is that they used only one position which did not allow the wire to hang straight down, Which? said.

Not surprisingly, mobile phone maker Ericsson played down the new findings in a public statement.

Which? said it was impossible to recommend a "safe" position for holding a phone. Both short and long distances between the aerial and the earpiece produced increased emissions, with only a short length in the middle generating lower emissions than conventional mobile phone calls. They recommend that "if you're concerned, the most important safety-first advice is to keep the number and duration of calls to a minimum, whether you use a phone with or without a hands-free kit