Men who use mobile phones could be risking their fertility, warn researchers.

A new study shows a worrying link between poor sperm and the number of hours a day that a man uses his mobile phone.

Those who made calls on a mobile phone for more than four hours a day had the worst sperm counts and the poorest quality sperm, according to results released yesterday at the American Society for Reproductive Medicine annual meeting in New Orleans.

Doctors believe the damage could be caused by the electromagnetic radiation emitted by handsets or the heat they generate.

The findings suggest millions of men may encounter difficulties in fathering a child due to the widespread use of mobile phones and offers another possible explanation for plummeting fertility levels among British males.