"We have been told to pay particular attention to females who may have concealed hidden explosives in their breasts," the airport worker said.
"This is particularly difficult for us to pick up but we are on a very high state of alert." The warning has led to long lines at Heathrow now near the end of summer travel season.
Since body scanners pick up objects outside the body, it's not clear whether women are being frisked by hand.
“They are taking longer to screen people and there is definitely some sort of profiling going on," said independent security analyst Paul Beaver.
Explosives expert Andy Oppenheimer said there is "great fear" that al-Qaida will put these medically-implanted explosives to use before too long.
"It’s pretty top secret and potentially very grisly and ghastly," Oppenheimer said.
