Electromagnetic waves are beamed onto passengers to create a 3-D image
A code of practice is being developed for airport body scanners in response to fears their images could break child pornography laws and privacy rights.
Civil rights groups have warned the scanners could produce illegal images of children and images of celebrities that could be leaked online.
But the Department of Transport said they were developing a staff code of conduct intended to allay these fears.
Gordon Brown has said the scanners are to be introduced at UK airports.
Terri Dowty, of civil rights group Action On Rights For Children, told the Guardian that the scanners could breach the Protection of Children Act 1978, under which it is illegal to create an indecent image or a "pseudo-image" of a child.
She said: "They do not have the legal power to use full body scanners in this way."
Ms Dowty added that there was an exemption in the 1978 law to cover the "prevention and detection of crime", but the purpose had to be more specific than the security measures being proposed by the government.
Simon Davies, of human rights campaign organisation Privacy International, also said he feared scans of celebrities or of people with unusual body profiles could prove an "irresistible pull" for some employees, leading to their potential publication on the internet.
But a Department for Transport spokesman said: "We understand the concerns expressed about privacy in relation to the deployment of body scanners.
"It is vital staff are properly trained and we are developing a code of practice to ensure these concerns are properly taken into account.
"Existing safeguards also mean those operating scanners are separated from the device, so unable to see the person to whom the image relates, and these anonymous images are deleted immediately."
Mr Brown had said travellers to and from British airports would see the "gradual" introduction of the use of full body scanners after Nigerian Umar Farouk Abdulmutallab, now in custody, was accused of trying to detonate a bomb on a plane bound for the US on 25 December.
'No silver bullet'
The scanners will initially operate alongside metal detectors, and be used for all flights in and out of the country.
The £80,000 full body scanners produce "naked" images of passengers.
They work by beaming electromagnetic waves on to passengers while they stand in a booth. A virtual three-dimensional image is then created from the reflected energy.
However, on Monday, a Tory MP warned the scanners would be "unlikely" to detect many of the explosive devices used by terrorist groups.
Ben Wallace, who used to work at defence firm QinetiQ, one of the companies making the technology, said the technology was not a "big silver bullet".
Mr Wallace said the scanners would probably not have detected the failed Detroit plane plot of Christmas Day.
A spokeswoman for QinetiQ said the technology "should be part of a layered approach to security".