The police have issued a warning for harassment against an airport worker after he allegedly took a photo of a female colleague as she went through a full-body scanner at Heathrow airport.

The incident, which occurred at terminal 5 on 10 March, is believed to be the first time an airport worker has been formally disciplined for misusing the scanners.

A Scotland Yard spokesman said: "Police received an allegation regarding an incident that happened at Heathrow Terminal 5 on March 10. A first-instance harassment warning has been issued to a 25-year-old male."

BAA said: "We treat any allegations of inappropriate behaviour or misuse of security equipment very seriously and these claims are being investigated thoroughly," a BAA spokesman said. "If found to be substantiated we will take appropriate action."

The incident is likely to reignite privacy concerns over the scanners by civil liberty groups. The Equality and Human Rights Commission last month warned that the government needed to take action to bring its policy for body-scanning passengers at UK airports within the law.

The commission said it had concerns about the apparent absence of safeguards to ensure the scanners were operated in a lawful, fair and non-discriminatory manner. It raised doubts as to whether the decision to install them at all UK airports was legal.

The scanners were introduced at Manchester and Heathrow last month after the Christmas Day bombing attempt over Detroit in the US. The £80,000 Rapiscan machines show a clear body outline and have been described by critics as the equivalent of "virtual strip searching".

While American transport authorities offer passengers a choice between going through the full-body scanner or going through a metal-arch scanner and a physical search, the British government has said that a refusal to go through the body scanner would bar passengers from boarding aircraft.

Earlier this month two women, one a Muslim, became the first people to be barred from boarding a flight at Manchester airport because they refused to go through a full-body scanner. The women, who were booked to fly to Islamabad with Pakistan International Airlines, were told they could not get on the plane after they refused to be scanned for medical and religious reasons.

A House of Commons home affairs committee report on airport security today welcomed the scanners' deployment and said it should have come sooner.

"Having witnessed these full-body scanners working at first-hand, we are confident that the privacy concerns that have been expressed in relation to these devices are overstated and that full-body scanners are no more an invasion of privacy than manual "pat-downs" or searches of bags," the committee said.

"Air passengers already tolerate a large invasion of their privacy and we do not feel that full-body scanners add greatly to this situation. Privacy concerns should not prevent the deployment of scanners."

• This article was amended on 11 June 2010 to remove information about a BAA employee, along with a quote, reported from another media source, that has since been contested