Trans people may suffer a breach of their privacy if compulsory body scanners are used in airports, the equalities watchdog has warned.

The Equality and Human Rights Commission (EHRC) has written to home secretary Alan Johnson to warn that use of the controversial scanners may breach human rights.

The scanners are to be introduced across British airports following a failed attempt by a man to blow up a plane flying over the US on Christmas Day.

They clearly show the naked body through clothes, including genitals, breast implants and intimate piercings.

According to the EHRC, this will have a “negative impact” on privacy for a number of groups, including trans people, children, women, disabled people and the elderly.

The body has asked Johnson for more details of privacy safeguards and how people will be selected for scanning, citing concerns about racial and religious discrimination.

The government has tried to placate critics of the technology by saying that images will be viewed only by a single security officer in a remote location before being deleted.

However, it is feared that celebrities or those with unusual physical features may find their scans appearing on the internet. The scanners may also breach laws on indecent images of children.

John Wadham, group director legal at the EHRC, said: “The commission fully accepts the government’s responsibility to protect the safety and security of air travellers. The right to life is the ultimate human right and we support the government reviewing security in the light of recent alleged terrorist activity.

“However, the government needs to ensure that measures to protect this right also take into account the need to be proportionate in its counter-terrorism proposals and ensure that they are justified by evidence and effectiveness.”