The findings have led to a leading British fertility expert to advise men to stop being addictedto mobile phones.

The study - by highly respected specialists - found that sperm levels of men who kept their phones in their pocket during the day were seriously affected in 47 per cent of cases compare to just 11 per cent in the general population.

Professor Martha Dirnfeld, of the Technion University in Haifa, said: "We analysed the amount of active swimming sperm and the quality and found that it had been reduced.

"We think this is being caused by a heating of the sperm from the phone and by electromagnetic activity."

The team monitored more than 100 men attending a fertility clinic for a year.

They found that besides men keeping their phones close to their groin many spoke on the phone while it was charging and kept it only a few centimetres from their bed.

Even keeping the phone on a bedside table appears to raise lower sperm cell counts.

The findings are in the journal Reproductive BioMedicine and support a long-feared link between dropping fertility rates in men and the prevalent use of cellular phones.