Research into the low-power microwaves used in calls every day discovered they can damage body cells and permanently alter DNA, leaving a potential health timebomb for millions of mobile phone users. The EU-backed study also found the risk of harm increased when phones are used in areas with poor signal because the hand-set needs higher-powered radiation to maintain contact with the network. Campaigners said the study provided further evidence of the dangers of mobiles and warned of the potential health crisis that could mirror the BSE/CJD timebomb.