The Equality and Human Rights Commission (EHRC) has said that airport scanners being used in Heathrow and Manchester invade people's right to privacy and break UK law.
The EHRC has written a letter to transport secretary Lord Adonis acknowledging that the government has to take steps to protect the travelling public from terrorist attacks, but arguing for more safeguards to ensure that the body scanners are operated in a lawful, fair and non-discriminatory manner.
Specifically, the organisation wants to see more evidence that the scanners comply with equality legislation, including the Race Relations Act, the Sex Discrimination Act and the Disability Discrimination Act.
"Without careful and formal consideration of the equality implications of this decision, for example through a full equality impact assessment, there is a serious risk that a measure introduced to protect the travelling public will have unintended discriminatory consequences," said the letter.
Home secretary Alan Johnson has said that passengers will be selected on a random basis to be scanned, but the EHRC has claimed that this is an empty promise because the airports are not monitoring who is being scanned.
"State action like border checks, stop and search and full body scanning are undertaken for good reasons," said EHRC chairman Trevor Philips. "But without proper care such policies can end up being applied in ways which discriminate against vulnerable groups or harm good community relations."
The EHRC is also concerned that the scanners conflict with the right to privacy under Article 8 of the European Convention on Human Rights.
"National security policies are intended to protect our lives and our f reedoms, but it would be the ultimate defeat if that protection destroyed our other liberties," said Philips.
Heathrow and Manchester airports started using the scanners on 1 February, and others, including Birmingham, will follow later this month.
The introduction of the scanners follows an attempted bomb attack on a US-bound plane from Europe before Christmas.
The technology has always been contentious because it produces effectively naked images, but the controversy deepened when a US privacy organisation pointed out that the scanners can store and transfer the images.
Further problems erupted a couple of weeks ago when Bollywood star Shahrukh Khan claimed that female staff at Heathrow airport had printed naked images of him as he walked through the scanners, and circulated them after he had added his autograph.
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