 Smartphone-using travellers, who have long suspected that charges for accessing data overseas are a rip-off, have found an unlikely ally - the chief executive of one of Britain's leading mobile-phone networks.  From July 2012, the wholesale cost of data - essential for browsing the internet, sending and receiving emails, and using social networking sites - is to be capped at 26p a megabyte (MB) across the EU, and the retail cost to consumers at 81p a MB. The intention is to limit what the competition commissioner, Neelie Kroes, has called the "outrageous profit margins" enjoyed by telecoms operators. Now David Dyson, the chief executive of Three UK, has called for far deeper price cuts.  "We support the European commission's objective of bringing the cost of roaming data down to UK levels, but to achieve that they need to go further," he said. "They should focus on driving wholesale rates down to three cents (2.6p) a megabyte or less."  The call comes as research from Heilbronn University, in Germany, revealed that two in three British travellers routinely switch off the data-roaming facility on their phones. Those who don't risk what the industry calls "bill shock" - in one case, Robin Bayne, from Chester-le-Street, Co Durham, received a ?4,000 data bill after a two-week trip to america. When he claimed he had been misled on charges, the service provider, Orange, reduced the bill to ?500.  With electronic guidebooks, podcasts, travel apps and mapping technology revolutionising tourism, smartphones are now second only to passports as a travel essential - but the costs soon add up. The fee for 1MB of data overseas is between ?1 and ?8, depending on your location and provider. That will give approximately 15 minutes on Google Maps or 30 emails at 34kb each.  None of the phone companies we called would reveal its mark-up on data-roaming fees, but the discrepancies between charges in this country and overseas are staggering. O2 customers can buy 1 gigabyte (1024MB) of data access in Britain for ?10. Outside Europe, the company can charge as much as ?6,144.  So, is there a way to beat the rip-off charges? Yes. In fact, there are four:  For zero fees, switch off data roaming before you leave the country - on an iPhone, go to Settings, then General, then Network.  Use your provider's pay-per-day package.  Vodafone's Data Traveller, for example, cuts the cost to ?2 for 25MB.  Make use of local wi-fi hot spots. If your phone is unlocked, buy a local Sim card that gives access to data services.  chris.haslam@sunday-times.co.uk  Controversial full-body scanners of the type used at Heathrow airport have been found to fail up to 54% of the time in trials at Hamburg and two australian airports. The L3 ProVision scanner uses high-frequency radio waves - known as millimetre waves - to see through clothing and detect hidden items. Yet studies in Sydney and Melbourne involving 23,500 passengers showed false readings in as many as four in 10 scans.  Despite the apparent unreliability of the machines, which cost about ?62,500 each, Paul Retter, executive director at the australian Office of Transport Security, said they would be deployed at the country's eight international airports. That won't be the case in Germany, where a year-long trial of more than 800,000 passengers returned a failure rate of 54%, with alarms triggered by zips, folds in clothing and even perspiration. Hans-Peter Friedrich, the interior minister, has shelved plans to roll out the scanners.  Meanwhile, Heathrow said: "The trial is ongoing, so we're not yet in a position to provide comment."  OVERHaUL FOR QM2  Cunard has announced a large-scale refurbishment of the Queen Mary 2, starting on November 24. Since its launch in 2004, the company flagship has received  