A US privacy organisation claims to have uncovered evidence that the full body scanners used by airports for security purposes, and which record effectively naked images of passengers, have the capability to store and transfer images.
The US has been using the scanners for a couple of years, but recently issued plans to step up their use following an attempted bomb attack on a US-bound plane from Europe before Christmas.
The UK, which has not used the scanners before, will introduce the first devices in Heathrow within the next couple of weeks.
Both countries argue that the scanners offer greater protection to passengers, while having little impact on privacy owing to the large number of protective controls supposedly applied.
The US Transport Security Administration (TSA) states on its web site that the technology "cannot store, print, transmit or save the image" and that "all machines are delivered to airports with these functions disabled".
Meanwhile, Andrew Andonis, UK secretary of state for transport, said last week that the UK will bring in a code of practice to deal with privacy issues, although the department could not elaborate on what this would involve.
However, the Electronic Privacy Information Center has obtained documents from the US Department of Homeland Security which reveal that the scanning machines hold capabilities which contradict the TSA statements, and raise serious concerns about the UK implementation.
The documents run to more than 250 pages long and contain the vendor contracts for so-called Whole Body Imaging devices. They reveal that the devices have hard disk storage, USB access and Ethernet connectivity.
The documents also detail a 'Level Z' authority for the TSA that allows the security agency to disable privacy filters and export raw image files.
A spokeswoman for the Department for Transport said today that the government can still give no indication of the privacy controls the UK will enforce when implementing the systems.
"Discussions are ongoing with the industry," she said.
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