Radiation from mobile phones may allow toxic chemicals to leak into the brain, a new study suggested yesterday.

The research from Finland, although at an early stage, strengthens fears that mobiles could be harmful to health.

A study of rats by a French team is said to support the evidence by indicating that mobile phone radiation can weaken the natural "blood-brain barrier" that protect the brain from poisons.

The Scandinavian study was led by Professor Darius Leszczynski, of the Radiation and Nuclear Safety Authority in Finland.

Professor Leszczynski said: "I would not yet say it is worrying, because we are not rats.

"But in my opinion this research does justify putting more money into human studies to find out whether this is a real danger."

He added that for the time being he had no qualms about using a mobile phone.

More than 40 million people, many of them children, in Britain have mobile phones.

Two years ago a Government inquiry led by Sir William Stewart concluded that mobile phones posed no provable health risk.

But Sir William urged caution over the use of mobile phones by children until more was known about their impact on health.

Dr Michael Clark, science spokesman at the National Radiological Protection Board - Britain's radiation hazard watchdog - said: "This is good work, but the Stewart group was well aware of the possibility of biological effects.

"You can't go straight from a biological effect to a health effect. It's a big leap."

The Federation of the Electronics Industry, which represents mobile phone manufacturers, declined to comment.

The Consumers' Association said there was still insufficient evidence to say whether or not mobile phones were safe.

A spokesman said: "At the moment, it's too soon to reach a definitive verdict on health risks from mobile phones, but neither has research given it the all-clear.