The new study shows that having a mobile phone close to the testicles - or within a foot or two of the body - can lower sperm levels so much that conceiving could be difficult.

The findings have led to a leading British fertility expert to advise men to stop being addicted to 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."