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A major international health study has shown that excessive mobile phone use can be linked to four different kinds of cancer.

The research, which has taken 10 years and cost £20million, found that heavy mobile users suffered up to 50 per cent more tumours.

Scientists now say there is a "significantly increased risk" of people developing three different kinds of brain tumour and one of the salivary gland. News of the findings, which are to be published within the next eight weeks, has led to calls for mobiles to carry health warnings.

Alasdair Philips, of campaign group Powerwatch, said: "Mobile companies hide the figures on how much radiation they give off in the back of manuals.

"But modern phones give out 217 electromagnetic pulses every minute into your head. Primary school children should not have them, secondary school children should be encouraged to text rather than call, and males should not keep them in a pocket because they drastically affect fertility."

The research has been done by the Interphone project, funded by the World Health Organisation and mobile phone companies.

Previous studies have been inconclusive, but Interphone draws together the most recent research from 13 countries and involved interviewing 12,800 people.

Dr Elisabeth Cardis, head of the study, said: "I am globally in agreement with the idea of restricting the use by children, though I would not go as far as banning mobiles."

The Department of Health has not updated its guidance in four years, saying only children should be "discouraged" from too many calls.

What you need to know

Is it safe to use my mobile?

Studies of people who have been using them for 10 years or more are coming out, showing worrying trends that heavy users are more likely to get brain tumours, so try to restrict calls or use hands-free.

Why do our bodies absorb phone rays?

Mobile phones transmit rays in all directions because the nearest mast could be anywhere.

Why are children more at risk?

They have thinner skulls and smaller brains, which absorb more radiation.

Will a mobile in my pocket damage sperm?

Yes. One study shows heavy use lowers sperm count by 30 per cent.

Should my child sleep with his mobile under his pillow?

No. Phones should be kept at least a metre away, where the radiation they give off drops dramatically.

What about keeping a mobile by my bed as an alarm clock?

It is best to switch it off completely. Even just sitting there, it sends a signal to the nearest mast every few minutes.

Would a hands-free kit make my phone safer?

Most Bluetooth kits cut radiation by up to 90 per cent. But check first - some handsets have HIGHER levels.

What about phone masts?

Scientists think they are a much lower risk than handsets - radiation is around 1,000 times smaller, the World Health Organisation says.

Is texting safe?

Texting is much safer than making phone calls.

What other countries do

In France, operators must offer parents text message-only models and advertising mobiles to under-12s is banned.

Australia's children are advised to use mobiles only in "extreme emergencies" and to turn them off at night.

Israel's government discourages the use of mobiles on public transport. And in Germany, low-emission phones have a "blue angel" mark, making it easier to choose safer models.